Forensic Firearms Evidence: Forensic Firearms Evidence Elements of Shooting
Incident Investigation melcon s. lapina Basic Firearms Design, Nomenclature and Operation: Basic Firearms Design, Nomenclature and Operation melcon s. lapina Slide3: A very basic firearm can be constructed from a piece of pipe with one end capped off, a firecracker and a marble or stone of sufficient size to drop down the pipe and in front of the firecracker. Indeed the earliest firearms of the 14th century were little more than this. The following figures show an abbreviated evolution from the hand cannon to contemporary firearms using self-contained metallic cartridges. In all of these forms the basic principle has remained unchanged: a projectile in a tube is expelled by the force of expanding gases generated by the very rapid burning of a propellant charge. melcon s. lapina Hand Cannon: Hand Cannon melcon s. lapina Slide5: By the 1300's cannons were known to exist in Europe and by the end of that century the first use of the term hand gun appeared in English records. The HAND CANNON lacked any wooden stock or trigger (lockwork) mechanism. The black gunpowder charge in these muzzle loaded firearms was ignited through a touch hole with some burning or smoldering object much like their larger counterparts. During the next two centuries various mechanical mechanisms were invented to ignite the powder charge in the gun (e.g..- matchlock, wheel lock and flintlock). Wooden stocks and sights were added to improve the handling and sighting of these smoothbore muskets. melcon s. lapina Flintlock : Flintlock melcon s. lapina Slide7: The FLINTLOCK is noteworthy for several reasons. It is the type of firearm used in the American Revolution, by the early settlers and by famous historical figures such as Davy Crockett and Daniel Boone. A renewed interest in these early firearms has resulted in numerous companies manufacturing modern replicas of such guns -- both rifled and smoothbore. While their use in crimes is essentially nonexistent, they may be encountered in accidental shootings or injuries. melcon s. lapina Percussion Lock: Percussion Lock melcon s. lapina Slide9: In PERCUSSION guns the flint and frizzen of the flintlock were replaced by a threaded hollow cone or nipple  onto which the shooter placed a copper cup (percussion cap  containing an impact sensitive explosive (originally mercury fulminate). At impact the percussion cap is crushed between the hammer and nipple, the explosive in the cap detonates and sends a jet of flame through the vent in the nipple  and into the black powder charge in the firing chamber. melcon s. lapina Slide10: This system was used in the early and mid 1800's, the Civil War and in the early West. Nearly all of these guns have rifled barrels which greatly improved accuracy. The first Colt and Remington revolvers frequently depicted in Western movies also used the percussion cap system of ignition. These guns were considerably more reliable than their predecessors and continue to be manufactured in the form of replica guns. Some of these reproduction guns have been used in crimes therefore a basic understanding of their workings is of forensic value. melcon s. lapina Slide11: The invention of the percussion cap and the greatly increased efficiency of breech loading designs in the mid 1800's lead to the development of RIMFIRE and early CENTERFIRE cartridges. Although numerous rimfire cartridges were developed in the last half of the 1800's only a few are still manufactured and in common use. melcon s. lapina Rimfire : Rimfire melcon s. lapina Slide13: The most noteworthy however is the very popular and ubiquitous 22 caliber rimfire. In RIMFIRE cartridges the primer mixture is deposited around the interior surface of the rim of the cartridge. The impact of the firing pin anywhere on the rim of the cartridge detonates the priming composition as the relatively soft metal of the rim is crushed by the firing pin. Because the metal of the rim must be sufficiently soft and thin to be pinched between the firing pin and the rear of the breech, this design is limited in the internal pressures it can withstand. melcon s. lapina Slide14: To achieve higher velocities CENTERFIRE cartridges were developed. Such cartridges contain the priming mixture in a centrally located soft metal cup (primer) with one or two vents (flash holes) leading into the interior of the cartridge where the powder charge is located. Variations in centerfire cartridges largely relate to the shape and length of the cartridge and, more importantly, the design of the head of the cartridge and the means by which the particular firearm positions and secures the cartridge in its chamber. melcon s. lapina Rimmed : Rimmed melcon s. lapina Centerfire : Centerfire melcon s. lapina Slide17: Two examples of centerfire cartridges are illustrated above. The RIMMED cartridge in this example has two (2) flash holes and is therefore of the Berdan-type priming system while the centerfire cartridge on the right has one (1) centrally located flash hole and is of the Boxer-type priming system. melcon s. lapina Slide18: melcon s. lapina Slide19: melcon s. lapina Basic Types of Handguns: Basic Types of Handguns melcon s. lapina Slide21: REVOLVERS all possess a cylinder in which multiple chambers (typically 5 or 6) have been machined to hold the cartridges. The cylinder revolves to the next firing position with each cocking of the gun's hammer (single action mode) or cycling of the trigger (double action mode). Cartridges for revolvers are usually of the rimmed type and remain in cylinder after firing until such time that the shooter removes them. Revolver mechanisms may be either single action or double action. Revolvers that are strictly single action are typified by the frontierstyle "six-shooter". melcon s. lapina Slide22: These guns all have an external hammer which must be manually cocked before the gun can be fired by pulling the trigger. The term single action relates to the fact that pulling the trigger accomplishes only one thing: release of the hammer from the cocked position. melcon s. lapina Slide23: Double action revolvers may possess an external hammer or be or hammerless. Most double action revolvers with external hammers can be manually cocked and fired in the previously described single action mode. By design, all double action revolvers can be fired by simply pulling the trigger without previously cocking the gun. In this mode of operation several things are accomplished thus the term "double action". As the trigger is pulled through its long cycle, the cylinder will advance and align the next chamber with the axis of the bore. melcon s. lapina Slide24: The hammer, whether external and visible or located within the lockwork of the gun ("hammerless"), is also being cocked back by continued pulling of the trigger. Finally at the end of the cycle as the trigger reaches its full rearwardmost position the hammer will fall and discharge the cartridge in the aligned chamber of the cylinder. melcon s. lapina Slide25: Due to the multiple events being accomplished in the double action mode, the force that must be applied to the trigger is much greater than that necessary to simply drop the hammer from its cocked position in single action mode. Double action trigger pulls are typically 10 to 12 lbs. as compared to 3 to 5 lbs. for single action firing in most contemporary revolvers. melcon s. lapina Revolvers : Revolvers melcon s. lapina Slide27: Two of the most common methods of loading and unloading revolvers: the top-break and the swing-out design. Swing-Out and Top-Loading melcon s. lapina Autoloading Pistols: Autoloading Pistols ("Automatics") all take cartridges from a magazine (often mistakenly called a "clip") located in the grip of the pistol. Upon discharge the slide moves rapidly rearward. The fired cartridge case is extracted from the chamber and ejected from the action of the gun as the slide reaches the end of its rearward cycle. melcon s. lapina Slide29: The gun's firing mechanism (internal striker, internal or external hammer) is also recocked during this portion of the slide's cycle. An internal coil spring returns the slide to its forward and closed position and in so doing strips the next cartridge from the magazine and loads it into the chamber. melcon s. lapina Slide30: This cycle takes place with each pulling of the trigger and discharge until the ammunition supply in the magazine is exhausted. Some autoloading pistols have a special latching system which will hold the slide back after the last shot is fired to signal the shooter that the pistol is empty. Shown below are two classic semiautomatic pistols (the U.S. model 1911 Colt .45 automatic and the German P'08 9mm Parabellum [Luger]) and one contemporary pistol (the Austrian Glock 9mm). melcon s. lapina Typical Autoloading Pistols: Typical Autoloading Pistols melcon s. lapina Slide32: Contemporary autoloading pistols typically have detachable magazines which are generally specifically designed for one particular make and model of pistol. In some magazines the cartridges are stacked in line directly on top of each other (e.g.- the two magazines on the left of the illustration below). In modern high capacity pistols the cartridges are staggered and some manufacturers' magazines may provide a means of counting the number of cartridges in it. melcon s. lapina Slide33: Once loaded, a detachable magazine is inserted in the butt of the pistol. If this is done with the slide forward, it must then be manually retracted to load the first cartridge into the chamber of the pistol. Some turn-of-the-century semiautomatic pistols were manufactured with a fixed magazine in their grips. With these guns the cartridges are typically inserted from above with a stripper clip and the stripper clip either discarded or recharged at some later time to be used again. melcon s. lapina Automatic Pistol Loading: Automatic Pistol Loading Representative Pistol Magazines melcon s. lapina Slide35: Loading a Fixed- and a Detachable Magazine Pistol melcon s. lapina Slide36: Loading the First Cartridge into the Chamber melcon s. lapina Common Methods of Operation: Common Methods of Operation There are at least a dozen operational systems in existence for the extraction, ejection and reloading of semiautomatic pistols. The most common will be described here. The straight or simple blowback design is used in 22 rimfire pistols and semiautomatic rifles. It is also used in nearly all centerfire semiautomatic pistols through 380 automatic caliber and in a few pistols chambered for 9mm Parabellum (Luger.) melcon s. lapina Slide38: In a straight blowback design the breechblock (slide in a pistol and bolt in a rifle) is simply held against the head of the cartridge in the chamber of the gun by spring pressure. The mass of the slide is much greater than that of the bullet. When the cartridge is fired the slide (or bolt) and the bullet are accelerated away from each other by the tremendous pressure generated by the burning gunpowder. This is depicted in the first figure below. melcon s. lapina Slide39: The heavier slide under opposing spring pressure only achieves a fraction of the velocity of the departing bullet but it is sufficient to allow the spent cartridge to be literally blown out of the chamber and to ultimately strike an ejector. This knocks the fired cartridge clear of the action before the recoil spring drives the slide or bolt forward again. melcon s. lapina Slide40: Blowback System melcon s. lapina Slide41: This very popular and widely imitated system is used in numerous makes and models of centerfire pistols chambered for the larger and more powerful cartridges such as 9mm Luger, 40 S&W, 10mm and 45 caliber automatic. melcon s. lapina Slide42: In this system the barrel is housed inside the full length slide. During discharge the two are locked together with one or more ribs on the barrel seated into corresponding grooves in the inside-top of the slide. Since the breech block is a part of the slide, both slide and barrel are thrust rearward when such a gun is fired. After traveling together a short distance during the period of high breech pressure a link attached to the rear of the barrel halts the barrel's rearward movement and pulls it down and out of engagement with the slide. melcon s. lapina Slide43: By the time this occurs the bullet has already left the barrel and the brass cartridge case has started to contract from the walls of the chamber. The slide however continues rearward extracting and ejecting the fired cartridge and compressing the recoil spring. The stored energy in the compressed recoil spring is now used to drive the slide forward, loading the next cartridge and relocking the slide and barrel together as the cycle is completed. melcon s. lapina Locked Breech System: Locked Breech System Before firing: Barrel and slide are locked together. melcon s. lapina Slide45: After firing: Slide has moved back, and unlocked from the barrel. The spring is now compressing. melcon s. lapina Modern Ammunition and Its Component Parts: Modern Ammunition and Its Component Parts melcon s. lapina Slide47: Virtually every portion and constituent of contemporary ammunition has potential evidentiary value - the propellant, the elemental makeup of the projectile and primer mixture, the design characteristics of the bullet, the wads from shotgun shells and a number of other features are all capable of resolving forensic issues which frequently arise in subsequent litigation. melcon s. lapina Slide48: A basic knowledge of these components and their potential evidentiary value is of critical importance for the success of an investigation of a shooting incident. melcon s. lapina Bulleted Cartridges: Bulleted Cartridges melcon s. lapina Slide50: melcon s. lapina Slide51: melcon s. lapina Class Characteristics of Rifled Barrels: Class Characteristics of Rifled Barrels melcon s. lapina Slide53: GROOVE width my be equal to-, less then- or greater than the width of the LANDS.
LAND widths are inversely related to the widths of the GROOVES i.e.- as wider grooves are cut the lands will become narrower. melcon s. lapina Slide54: The caliber designation of a firearm in the United States has most frequently been expressed in terms of either the bore diameter (d in the illustration above) or the groove diameter (D) in either hundredths or thousandths of an inch. The naming of cartridges always begins with the caliber of the firearm followed by additional descriptive information as pointed out earlier in this monograph. melcon s. lapina Slide55: The following 30 caliber cartridges were named on the basis of bore diameter (d): .30-40 Krag., .30-'06. .300 Savage and .300 Winchester Magnum. The barrels of all of these guns have nominal bore diameters of .300 inches. The depth of each groove in most 30 caliber U.S.-manufactuned firearms is about 0.004 inches therefore the groove diameter (D) of these barrels will typically measure .308 inches (i.e.. - D=.300+.004+.004). melcon s. lapina Slide56: Some manufacturers of 30 caliber firearms have elected to name their cartridges on the basis of groove diameter rather than bore diameter. Examples are the .308 Winchester and the .308 Norms Magnum. The bullets for all six of these guns will measure .308 inches in diameter. melcon s. lapina Slide57: An ammunition company or a handloader could, therefore, load the same 180 grain 30 caliber bullet in each one of the different cartridges used as examples in this discussion. The only distinction after that would be upon discharge. Some of these bullets would achieve greater muzzle velocities due to the greater powder capacities of certain cartridges compared to others (e.g..- the .30-40 Krag vs the .300 Winchester Magnum with muzzle velocities of approximately 2430 feet per second vs. 2960 f/s respectively.) melcon s. lapina Slide58: "Grains" are the units of bullet weight commonly employed by U.S. manufacturers. One grain equals 1/7000th of a pound. Nearly all other sources of ammunition will express bullet weight in grams. One gram equals 15.4 grains. melcon s. lapina Slide59: American manufacturers have named some of the more recent cartridges on the basis of the metric designation which is in keeping with the majority of other countries. Examples of American-designed cartridges with metric caliber designations are the 6mm Remington, the 7mm Weatherby Magnum and the 10mm Automatic. U.S. military cartridges have also adopted the metric method of caliber designation. The two service cartridges in present use were originally sporting cartridges and have simply been given metric designations: .223 Remington = 5.56mm and .308 Winchester = 7.62mm NATO. melcon s. lapina Summary : Summary In summary, the caliber designation of a firearm or cartridge may be based on one of several means of measurement. Some of these bear little relevance to the bore or groove diameter of the guns that were designed to fire the particular cartridge. Examples of these anomalies are the well-known 38 Special and 44 Magnum. The groove diameter of most 38 Spl. firearms (and therefore the bullet diameter of most 38 Spl. bullets) is. 357 inches. The diameter of most 44 Magnum bullets will measure .429 to .430 inches. melcon s. lapina Slide61: These revelations are not intended to confuse or befuddle the reader. Rather they are meant to serve as a caution that he or she may need the assistance of a competent guide to help him or her fully understand the particular details of the firearm or firearmsrelated evidence associated with the case under investigation. Finally, some manufacturers and some countries have given different names to the same cartridge, e.g., the 380 Automatic is the same as the 9mm Kurz in Germany. melcon s. lapina Slide62: A cartridge interchangeability chart taken from the 1991 Remington ammunition brochure has been included in this handbook as an excellent guide on this subject. Remington's illustrated table of cartridge ballistics for centerfire rifle cartridges and for pistol/revolver ammunition have also been included as useful aids in understanding the characteristics of modern ammunition. melcon s. lapina Common Rifling Systems and Configurations: Common Rifling Systems and Configurations In traditional rifling the manufacturer will have cut or formed an even or odd number of grooves in the bore of the barrel. Cross-sectional views of a 5 and 6 grooved bore are shown below. A number of manufacturing methods are available to form these grooves. In some methods the grooves are cut by a cutting or broaching tool. In others they are swaged of forged into the metal. The grooves in the bore will also turn either clockwise or counterclockwise with twist rates on the order of 1 turn in 10 to 20 inches for most common firearms. Rotation of the rifling is necessary to spin-stabilize the fired bullets for their flight through the atmosphere. melcon s. lapina Slide64: 5 LANDS and GROOVES
(ODD) melcon s. lapina Slide65: The actual twist rate for a particular bullet/cartridge design is chosen on the basis of certain exterior ballistic requirements. There is no special advantage to the particular direction of rotation. The convention regarding direction of rotation is to describe twist as either right (clockwise rotation) or left (counterclockwise rotation). melcon s. lapina Slide66: This will be discussed in more detail in a subsequent paragraph. Inspection of the two cross-sectional views of the traditional rifling profiles above will reveal that one cannot have a greater or lesser number of lands and grooves, i.e.- the cutting of 4, 5 or 6 grooves leaves as a consequence 4, 5 and 6 lands respectively. melcon s. lapina Slide67: Therefore, when examining the bore of a rifled firearm, it is the viewer's choice as to which he or she finds easier to count; lands or grooves. Manufacturers also have some choice as to how wide they wish to make the grooves. It should be apparent after studying these barrel cross-sections that there is an inverse relationship between land width and groove width. melcon s. lapina Slide68: As the grooves are made wider the lands must become correspondingly narrower. This fact coupled with some basic properties of circles gives rise to a very useful relationship between the bore diameter (land diameter), the number of grooves and the widths of the lands and grooves. melcon s. lapina Slide69: If one draws straight lines across each land and groove for any arrangement of a traditional rifling profile, a polygon will be formed with corners on a circle whose diameter is equal to the land diameter. The reader who wishes to prove this to himself need merely complete the dashed lines on the 4 groove bore. melcon s. lapina Slide70: If N is the number of grooves, L equals the landwidth and G equals the groove width, the resultant polygon will have a circumference equal to (L+G) x N. This circumference will be slightly less than that of the circle in which the polygon is confined. Since the circumference of a circle is πd, this approximation can be expressed as follows:
(L+G)N ≈ πd
Where d is the bore diameter;
(also the distance from land-to-land.) melcon s. lapina Slide71: L+G ≈ πd/N,
It can be seen that for a given caliber (d) and number of grooves (N), the sum of a land and a groove width must be nearly constant. It should also be apparent that the widths of the lands and grooves are interdependent as well as inversely related. melcon s. lapina Slide72: These mathematical approximations have special forensic value. In actual casework involving recovered projectiles, the bullets are frequently damaged during impact. If, for example, we recover a very out-of-round bullet of questionable caliber but we can discern that there are 6 groove impressions in it and we can get a width measurement on at least one land impression and one groove impression then the caliber (bore diameter) can be calculated. melcon s. lapina Slide73: Alternatively, we will encounter cases where the caliber is known but only one measurable land and groove impression have survived terminal ballistic damage. melcon s. lapina Slide74: Using the previously-described mathematical approximation, the number of lands and grooves (N) can be calculated. These interrelationships can also be reduced to a convenient table for the common handgun and rifle calibers. melcon s. lapina Slide75: The convention regarding direction of rotation of the lands and grooves is to describe twist as either a right twist (clockwise) or a left twist (counterclockwise). Direction of twist determinations are customarily made with the unaided eye and by directing one's attention to the upper surface of the bore while looking through it. The observer should note whether the lands (or grooves) curve away to the left (left twist) or to the right (right twist) as they proceed away from one's view. melcon s. lapina Slide76: Although most firearms are most easily examined from the muzzle end, it makes no difference from which end (muzzle or breech) one makes the determination so long as the foregoing instruction is followed. Shown on the next page are the most common configurations for traditional rifling. melcon s. lapina Slide77: Barrels have also been rifled with a lesser and greater number of grooves, e.g.- 2, 3, 10, 16, 20 and 22 grooves. Extensive compilations of guns of known rifling characteristics based on caliber, cartridge type, number of lands and grooves, direction of twist and increasing land width have been assembled by the FBI Firearms Unit and others. melcon s. lapina Common Rifling Configurations: Common Rifling Configurations 4-R 5-R 6-R 6-L 7-R 8-R melcon s. lapina Slide79: Such data bases provide a useful means of identifying the various makes and models of guns that could have fired a particular bullet in a "no gun" case. In some situations the list may be long where the general rifling characteristics are common to many guns in the particular caliber/cartridge type category. In other situations there may only be 1 or 2 types or models of guns rifled in a particular way, e.g., 380 Automatic/7-Right and 9mm Parabellum/4-Left. melcon s. lapina Slide80: Within the last decade another method of rifling gun barrels has been introduced. In this method there are no sharply defined land and groove edges. Rather a smooth transition occurs between the raised areas (lands) and the depressed areas (grooves) in the bore. This method has come to be called polygonal rifling. melcon s. lapina Six-Groove Polygonal Rifling Profile: Six-Groove Polygonal Rifling Profile melcon s. lapina Slide82: Presently (1991) it is used in the Austrian Glock pistols in 9mm, 40 S&W, 10mm Automatic and .45 ACP. Some semiautomatic pistols made by the Heckler & Koch firm of Germany also use this type of rifling with 4 grooves and a right twist whereas the Glock guns have used 6 groove/right twist configurations to date. The interior surfaces of these barrels are very smooth and therefore the markings they impart on fired bullets are very fine. This has often made the process of identifying bullets fired from such guns quite difficult. Examination of Fired Bullets for Firearm-Generated Class Characteristics: Examination of Fired Bullets for Firearm-Generated Class Characteristics melcon s. lapina Slide84: Before proceeding further it might be well to define Class Characteristics for the reader who is not a forensic scientist. Class characteristics are the intended features of an object. In the case of a rifled firearm they include caliber, chambering (cartridge type), number of lands and grooves, direction of twist and land and groove widths in the case of traditional rifling. melcon s. lapina Slide85: There are other features that would meet this definition (such as barrel length and twist rate) but it is only those class characteristics that express themselves clearly in fired bullets and expended cartridge cases that are of primary interest to the criminalist or firearms examiner. melcon s. lapina Slide86: Indeed a considerable portion of this presentation has involved the class characteristics of ammunition, ammunition components, propellants and rifled firearms and it has been for a good reason. Class characteristics provide us with an orderly means to sort and catalogue evidence; to quickly rule out certain sources and to narrow our investigative efforts to an ever dwindling group of possible sources. melcon s. lapina Slide87: An appreciation and basic understanding of the great variety in bullet types and construction, calibers and rifling characteristics of firearms becomes important in the investigation of shooting incidents. This is true at the scene of the incident, at the hospital or during an autopsy. melcon s. lapina Slide88: For example, bullet cores often become separated from the bullet jacket during impact and penetration. These cores may superficially look like a fired bullet even to the point of bearing the outline of the land and groove impressions. These are mere vestiges of the actual rifling marks and have simply printed through the bullet's jacket and into the underlying lead core. melcon s. lapina Slide89: It is, of course, the shed jacket that must be recovered in order to determine the caliber and brand of ammunition involved and to ultimately identify the responsible gun. Some of the newer jacketing materials (e.g.- the aluminum jacketed Silvertip projectiles made by Winchester) are not easily seen on x-rays if they separate from the bullet's core. The surgeon or pathologist may have to locate them by touch. melcon s. lapina Slide90: Whether a lead bullet or a jacketed bullet, upon discharge the bearing surface of the projectile takes up the image of the lands and grooves as it is driven down the bore by the substantial pressures generated by the propellant gases. Since the diameter of the unfired bullets are typically made to nominal groove diameter, the lands must displace bullet or jacket metal and will leave a grooved track where they gripped and spun the fired projectile. These land impressions are discernible with good near-vision or with the aid of a small hand magnifier. melcon s. lapina Slide91: Determining the direction of twist is a fairly simple matter and, as with looking through gun barrels, it doesn't matter whether you hold the bullet with its nose pointed away from you or towards you. Simply note whether the land impressions angle off toward your left or toward your right as they go away from you (see the illustrations.) melcon s. lapina Class Characteristics on Fired Bullets: Class Characteristics on Fired Bullets 1, 2 Two full metal jacketed bullets from a pistol having a left twist and land widths approximately one-half the groove widths (L≈1/2G). melcon s. lapina Slide93: A FMJ bullet fired from a pistol with a right twist and possessing lands approximately twice the width of the grooves ( L≈2G).
A round nosed lead bullet fired from a *revolver with a right twist, L≈G.
A semi-wadcutter bullet fired from a *revolver with a right twist, L=1/3G. melcon s. lapina Slide94: BASE TO BASE comparisons are useful in the field to determine -
A whether more than one weapon is involved.
B that bullets of the same caliber but different in brand or design could have been fired in the same weapon and –
C to determine the land and groove count on a badly damaged bullet by agreement with one in near-pristine condition. melcon s. lapina Slide95: Counting the number of land impressions is also something that can be accomplished with some practice and little or no special equipment beyond good near-vision and adequate lighting.
If multiple bullets are recovered from a scene or victim a simple base-to-base comparison will quickly reveal the involvement of more than one firearm even though the same type and caliber of ammunition was used (see example A in the illustration above). melcon s. lapina Slide96: Although somewhat more subtle, bullets fired from revolvers will frequently show a slight retracking or realignment of the land impressions where they first begin to grip the bullet . This is due to the unique design of revolvers wherein the bullets frequently enter the forcing cone and rifling at the beginning of the barrel after having exited the unrifled and slightly oversized chamber in the cylinder. melcon s. lapina Slide97: Any and all of these field-expedient observations must be carried out with great care and consideration for possible trace evidence that might be adhering to or embedded in the bullet. In some cases such things as embedded glass, paint, fibers, fabric imprints or bone particles may be of more importance than the matching of the bullet back to the responsible gun. melcon s. lapina Slide98: Recovered projectiles and projectile fragments should be carefully wrapped as recovered in a piece of clean dry paper towel or tissue and then secured in a suitable container. Cotton packing should not be used as a packing material since it will result in numerous cotton fibers adhering to the bullet or bullet fragments. Suggestions on marking such evidence are described in the back of this handbook. melcon s. lapina Marks Left by Firearms on Fired and Unfired Cartridges During Loading: Marks Left by Firearms on Fired and Unfired Cartridges During Loading Automatic, semiautomatic and repeating rifles and pistols which utilize a detachable magazine may leave magazine lip marks on the cartridge casings as they are stripped from the magazine and loaded into the chamber of the gun. These marks are caused by the forward lips of the magazine scraping the case wall and/or rim. melcon s. lapina Slide100: Magazine lip marks usually take the form of a shallow, slightly curved line along the side of the cartridge case as shown in the figure below or simply as two gouges on the rim approximately 120 degrees apart. melcon s. lapina Magazine Lip Marks: Magazine Lip Marks melcon s. lapina Slide102: Observing such marks on fired cartridge cases would strongly suggest that the responsible firearm takes cartridges from such a magazine. This is potentially useful information since there are alternative methods of feeding cartridges into the chamber of a gun (e.g.- tubular magazines) which do not have lips incorporated into their design. melcon s. lapina Slide103: It should also be pointed out that not all box magazines will necessarily leave magazine lip marks on cartridges stripped from them. When they are present they can frequently be identified as having been produced by a particular magazine. In assessing their value however, three very important facts must be remembered: melcon s. lapina Slide104: Such marks are produced during loading or removal of cartridges from a magazine. They are not a consequence of firing the cartridge in a particular gun.
They are associated with a particular magazine which is usually detachable and therefore could be inserted and used in numerous other firearms.
The absence of such marks does not preclude a magazine-fed firearm from having been used as not all magazines will scrape the cartridges sufficiently to leave visible marks. melcon s. lapina Breech Closure or Anvil Marks: Breech Closure or Anvil Marks These marks may be imprinted on the forward surface of the rim in rimmed and semi-rimmed cartridges such as the 22 rimfire, .25ACP, .32ACP, .38 ACP or Super (pistol cartridges) or rimmed rifle and machinegun cartridges like the .303 British and 7.62x54R Russian. They may occur when the rims of such cartridges impact the rear of the chamber as they are driven into battery by the force of the bolt in automatic or semiautomatic firearms. melcon s. lapina Slide106: Identifiable toolmarks associated with the particular gun may be imprinted in this area of the cartridge rim. If such marks are produced upon closure of the breech or bolt of the gun then it can only be said that the cartridge was at some time loaded into the firearm but not necessarily fired in it. In some 22 rimfire guns an anvil mark is produced when the firing pin crushes the rim of the cartridge against the supporting area at the back of the chamber. melcon s. lapina Slide107: The side of the rim opposite the firing pin takes up the toolmark pattern present in the metal of the particular firearm. The writer has observed this phenomenon in a number of Ruger 22RF semiautomatic pistols. In this situation the impressed toolmarks left in the front side of the cartridge rim are produced at the moment of discharge (see figure) and therefore can be used to identify a particular gun as having fired the expended cartridge. melcon s. lapina Anvil Marks on a 22 Rimfire Cartridge: Anvil Marks on a 22 Rimfire Cartridge melcon s. lapina Extractor Marks: Extractor Marks The extractor in a firearm usually takes the form of a small metal hook or claw-like fixture on the bolt of a rifle or the slide of a semiautomatic pistol whose function is to remove fired or unfired cartridges from the chamber. The forward hook portion of an extractor may leave marks on the edge of the rim of a cartridge, in the extraction groove of a cartridge or on she forward face of the cartridge rim. melcon s. lapina Extractor Mark Locations: Extractor Mark Locations melcon s. lapina Slide111: In certain types of guns the marks left by the extractor occur during the loading cycle. In other guns they are the consequence of the removal of the cartridge from the chamber. In many blowback operated guns such as 22, 25 and 32 caliber semiautomatics, the extractor may leave no discernible marks on fired cartridges because they are literally blown out of the gun's chamber upon discharge. melcon s. lapina Slide112: Although quite small, the toolmarks left on cartridge cases by extractors are capable of being associated with the particular gun and extractor that made them. The interpretation however, as to whether such marks were produced during loading, unloading or extraction after firing is an important one. melcon s. lapina Slide113: In certain types of semiautomatic firearms (by-in-large ones with inertia firing pins such as the 1911 and 1911A1 Colt automatic, copies of this gun, the 30M1 carbine and many others), the firing pin will frequently leave a small firing pin indentation mark in the cartridge primer when the slide or bolt closes in the normal manner. melcon s. lapina Slide114: This is usually due to the firing pin return spring being a little weak or fatigued from age which then allows the firing pin to coast on into the primer as the bolt or slide slams closed. melcon s. lapina Slide115: In certain types of semiautomatic firearms (by-in-large ones with inertia firing pins such as the 1911 and 1911A1 Colt automatic, copies of this gun, the 30M1 carbine and many others), the firing pin will frequently leave a small firing pin indentation mark in the cartridge primer when the slide or bolt closes in the normal manner. This is usually due to the firing pin return spring being a little weak or fatigued from age which then allows the firing pin to coast on into the primer as the bolt or slide slams closed. melcon s. lapina Slide116: This small indentation will subsequently be obliterated when the cartridge is actually fired. Its presence on unfired cartridges however, serves to establish their having been loaded into the firearm on some previous occasion. Such facts have forensic significance depending upon the nature of the case and any statements made by the person having possession of the gun. melcon s. lapina Rotating Bolt Closure/Opening Marks: Rotating Bolt Closure/ Opening Marks Certain centerfire semiautomatic rifles have bolts that rotate upon closure and locking of the breech, e.g., the 30M 1 Carbine, M 1 Garand, AR-15 /M 16 and others. The loading of a cartridge into the chamber or, more frequently the firing, unlocking and extraction of a cartridge from one of these guns will often leave a characteristic semicircular scrape mark on the head of the cartridge. melcon s. lapina Slide118: This is usually due to some slight roughness around the aperture in the bolt face for a pin-type ejector which causes a scrape as the bolt rapidly rotates during the unlocking cycle. An additional factor that favors the creation of such marks after, rather than prior to discharge is the considerable pressures created during discharge (often on the order of 50,000 psi) will have thrust the brass cartridge case back against the boltface within milliseconds of it rotating and opening. melcon s. lapina Slide119: Regardless of the specific mechanism in a particular firearm these marks can tell us much about the type of firearm that fired such cartridges before the gun is even recovered. Since these marks also often have individuality, they can serve as a means of identification just as with many other sources of unique toolmarks on recovered cartridges. melcon s. lapina Rotating Bolt Scrape Marks: Rotating Bolt Scrape Marks melcon s. lapina Marks Left on Fired Cartridges During Firing and Ejection: Marks Left on Fired Cartridges During Firing and Ejection With the previous example we transitioned from a source of marks left on a cartridge case as a consequence of loading to marks generated during discharge. We've also seen that some marks such as extractor marks may represent a combination of events during the loading and unloading cycle. The true causative mechanisms and interpretation of gun-generated marks on cartridge cases must, of course, be left to a competent firearms examiner. melcon s. lapina Slide122: My purpose here is to acquaint the reader with the numerous sources of marks left on cartridge cases, their ability to provide investigative leads and, in many cases, to associate a particular firearm with the expended or extracted cartridge. In this section the sources of marks on cartridges generated during and following discharge will be discussed and illustrated. melcon s. lapina Firing Pin Impressions: Firing Pin Impressions Firing pins may be manufactured in a variety of shapes. This is particularly true in the case of rimfire firearms. Hemispherical, circular (flat-faced), square, rectangular and even triangular firing pins have been used by various companies. Some of the more common forms of rimfire firing pin impressions are shown in the illustration in the next slide along with some of the class characteristic distinctions that can be measured in addition to the general shape. melcon s. lapina Rimfire Firing Pin Impressions: Rimfire Firing Pin Impressions melcon s. lapina Slide125: Less variety exists in certerfire firing pin shapes although there are some noteworthy exceptions such as the elongated wedge-like firing pin of the Glock series of semi-automatic pistols.
The machining and finishing processes used to manufacture firing pins typically leave unique toolmarks on them. These individual characteristics will frequently be left in the firing pin impressions in the rim of rimfire cartridges and the primers of centerfire cartridges at the moment of discharge. Such marks are often used to identify the responsible firearm as having fired the particular cartridge. melcon s. lapina Centerfire Firing Pin Shapes: Centerfire Firing Pin Shapes melcon s. lapina Slide127: Certain centerfire firearms due to their design will frequently leave a firing pin scrape mark. Locked breech semiautomatic pistols of the Colt-Browning design (e.g.Colt 1911 and 1911A1 45ACP, 9mm Browning Hi-Power, all S&W 9mm and 45ACP pistols, Ruger P-85, Glock pistols and others) often leave such a mark at the 12 o'clock position to the firing pin impression. This occurs when the firing pin fails to fully retract from the firing pin impression as the pistol recoils and the chamber end of the barrel is pulled downward out of its previously locked position in the slide. melcon s. lapina Slide128: Firing pin scrape marks may also occur with break open single and double barreled shotguns. With these guns the cause is usually a fatigued or defective firing pin return spring which allows the firing pin to remain partially inserted in the firing pin impression. Opening the action will cause the protruding firing pin to drag or scrape the struck primer at the 6 o'clock position as the barrel is tipped upward to the open position. melcon s. lapina Slide129: Observing such a mark on a fired pistol cartridge or shotgun shell reveals much about the mechanism of the firearm involved. Guns with other types of actions lacking this sort of opening and unlocking principle will not leave firing pin scrape marks on fired cartridges. melcon s. lapina Breechface Signature: Breechface Signature During firing the pressures exerted by the propellant gases driving the bullet up the bore and thrusting the cartridge head back against the breech or bolt face are typically 20,000 to 50,000 psi depending on the cartridge type and loading. Toolmarks from the milling and finishing processes present on the contacting surfaces are literally stamped into the relatively soft metal of the primer and head of the cartridge by the force of these pressures. melcon s. lapina Slide131: Since the specific pattern of these marks is unique to each firearm and they change very little if at all with time and repeated firings, these marks serve as the most useful, lasting and reproducible means of identifying expended cartridges and the guns that fired them. melcon s. lapina Slide132: The process used to manufacture a particular type of firearm may have a direct bearing on the type or style of toolmarks on the bolt or breechface of these guns. Recessed breechfaces by necessity must be cut out by some sort of rotary cutting tool. Such a process will usually leave circular toolmarks on the breechface. melcon s. lapina Slide133: Examples of such guns would be the wellknown German Luger and P-38 pistols of WW-II. The flat breechfaces of Colts, S&W's, Glocks and some other centerfire semiautomatic pistols will have parallel toolmarks running vertically on their breechfaces as a result of the milling and finishing methods used to manufacture them. melcon s. lapina Slide134: The general pattern of the breechface signature printed into the primer or head of a fired cartridge can usually be seen with the unaided eye with proper lighting. With the help of the subsequent illustrations it should now be apparent that a simple inspection of fired cartridges from a shooting scene could alert the astute investigator that more than one firearm was involved where there are two styles of breechface signatures even though the cartridges themselves may all be of the same brand and type. melcon s. lapina Chamber Striae: Chamber Striae These marks, when present, usually take the form of the striations running parallel to the axis of the cartridge case and tend to be more prevalent toward the rear of the cartridge. Chamber striae are generally associated with semiautomatic firearms of straight or simple blowback design. melcon s. lapina Slide136: This would include 22 rimfire semiautomatics, .25ACP, .32ACP and most .380ACP semiautomatic pistols. These striations arise from the partial extraction of the cartridge case from the chamber while the propellant gases are still accelerating the bullet and forcing the walls of the cartridge case out against the chamber walls. melcon s. lapina Slide137: Indeed this is the basic principle of the simple blowback design wherein the bolt or slide starts moving rearward as the bullet is being propelled forward. In locked breech guns such as bolt action rifles, lever action rifles, single shot rifles and pistols and revolvers the bullet will have exited and the internal pressures returned to ambient conditions before the action can be opened. melcon s. lapina Slide138: In this situation the fired cartridge will contract slightly before it can be removed from the chamber thereby reducing or even precluding the deposition of chamber striae on the body of the cartridge. melcon s. lapina Ejector Marks: Ejector Marks Ejection of the fired cartridge from a repeating firearm is most often accomplished by a small, protruding metal part usually mounted toward the rear of the loading/ unloading mechanism of the gun. This ejector strikes near or at the edge of the head of the extracted cartridge as it reaches the end of the extraction cycle. The impact of the ejector against the cartridge case knocks it clear of the gun's mechanism so that a new, unfired round of ammunition can be loaded into the chamber. melcon s. lapina Slide140: In manually operated firearms such as pump, lever and bolt action guns, the impactive forces created by the working of these actions frequently fail to leave an ejector mark of sufficient depth or clarity to either be recognized as such or to be identifiable as having come from a particular gun. Ejector marks on cartridges fired in machineguns, submachineguns and semiautomatic firearms are imprinted with much greater and more uniform shot-to-shot forces. melcon s. lapina Slide141: Such well-indented ejector marks are capable of being matched or associated with the specific firearm although firearms examiners seldom need to use them for this purpose since a much greater wealth of firearms-generated marks are produced by the firing pin and breechface. melcon s. lapina Slide142: The greater forensic value of ejector marks comes from their shape and location in relation to other markings on expended cartridge cases. The spatial relationship and orientation of the ejector mark, extractor marks and the breechface signature reveal much about the arrangement of these parts in the gun that fired the cartridge long before the gun is recovered. melcon s. lapina Slide143: This information, much like the General Rifling Characteristics (GRC) can be used to compile a listing of makes and models of guns that could have fired an evidence cartridge. When combined with the GRC of a recovered bullet, the list of possible guns in a "no gun" case will usually become much smaller. melcon s. lapina Slide144: Finally, one other type of mark may be left on fired cartridges as they are ejected from the gun's action. This mark usually takes the form of a small crease, scuff or indentation on the cartridge wall (see the Summary illustration). This type of mark occurs almost exclusively in full or semiautomatic firearms and is a consequence of the fired cartridge striking the edge of the gun's ejection port as it exists the gun. melcon s. lapina Slide145: With certain firearms this impactive interaction takes place in a very reproducible manner to the extent that identifiable toolmarks will be left on the fired cartridges. The following illustration summarizes all the various marks that may be left on an expended cartridge. melcon s. lapina Summary of Marks Left on Expended Cartridges: Summary of Marks Left on Expended Cartridges melcon s. lapina Slide147: The illustration on the preceding slide incorporates nearly all the various marks that may be found on fired cartridges from repeating firearms other than revolvers. Cartridges fired in revolvers will have a firing pin impression and breechface signature but will lack the other firearms-generated marks due to their design and method of operation. It should also be pointed out that it is uncommon to find cartridges from a revolver at a shooting scene if less than 5 or six shot were fired. melcon s. lapina Slide148: This illustration also shows one of the suggested locations for marking a recovered cartridge. Many agencies prefer that evidence cartridges be marked on the inside of the mouth. This is quite acceptable if it can be accomplished given the size of the cartridge and the capabilities of the finder. melcon s. lapina Summary of Firearms-Generated Marks on Cartridges: It is the field investigator and crime scene technician that stands to realize the greatest benefit from having some understanding and appreciation of the various marks left on fired cartridges and the sources of these marks. Summary of Firearms-Generated Marks on Cartridges melcon s. lapina Slide150: Certainly these marks and their origins are well-known to competent firearms examiners. But these individuals are seldom called to the scene of a shooting incident and they may not see the evidence that was collected until days, weeks or even months later when it is submitted for examination. melcon s. lapina Slide151: Field inspection of recovered cartridges can reveal much about the guns) that fired them beyond that of the caliber and cartridge type (e.g., 9mm Luger, 45ACP, etc.) The shape of the firing pin in the responsible gun can be reasonably deduced from the firing pin impression in the cartridge. Once any recovered guns have been processed and rendered safe it is not usually difficult to see the face of the firing pin, the location and shape of the ejector, the location of the extractor and the appearance of the finish on the breechface of the gun. melcon s. lapina Slide152: This type of field expedient evaluation may reveal a number of very important and timely findings. For example, it may quickly become evident that more than one gun is involved due to very different styles of breechface signatures on a group of cartridges of the same caliber and type. It may be apparent that are covered gun is not the gun being sought (e.g., circular breechface marks on a recovered cartridge) but the gun has parallel milling marks on its breechface. melcon s. lapina Slide153: There is however, one concept not previously discussed that must be understood. In attempting to compare the marks on the head of a fired cartridge with the breechface of a gun, one must contend with right-left reversal. The firearms-generated marks on the head of a fired cartridge are a reverse image of the breechface of the responsible gun. melcon s. lapina Slide154: One useful approach to take when inspecting questioned guns is to envision where the extractor and ejector would be if you could see through the gun as you hold it up at eye level and pointed away from you. This is the same view you have of the fired cartridge once it is rotated into proper position. These concepts are demonstrated in the illustrations below which depict the breechfaces of three (3) 9mm pistols and the expended cartridges from each. melcon s. lapina Slide155: Comparing
Breechface Marks melcon s. lapina Metallic Cartridge Design and Nomenclature: Metallic Cartridge Design and Nomenclature melcon s. lapina Slide157: There are three (3) general shapes for metallic cartridge cases:( 1 ) STRAIGHT (2) TAPERED and (3) BOTTLENECKED Cartridge Case Shapes melcon s. lapina Slide158: The tapered case form is essentially obsolete and is unlikely to be encountered in contemporary shooting incidents.
Most centerfire rifle cartridges are of the bottleneck type since this case form provides the greatest powder capacity to caliber ratio.
All .22 caliber rimfire cartridges and most centerfire pistol and revolver cartridges in current manufacture have straight cases. melcon s. lapina Slide159: In the United States and many other western countries (and countries importing ammunition to the U.S. for sporting and recreational shooting), the cartridges are made of brass. One U.S. company (Blount, formerly Omark Industries) offers a complete line of centerfire pistol and revolver cartridges with aluminum cases. In the Soviet Union, Eastern Europe and mainland China, cartridges are typically made of steel often with a thin copper plating or an epoxy-like varnish on their surface to inhibit rusting. melcon s. lapina Slide160: Primer ignition methods for centerfire cartridges will either be of the Boxer or Berdan type. Visual inspection of the interior of an expended cartridge in good light will usually reveal which type one has by the presence of a single, centrally-located flash hole [Boxer-type] or two (2) flash holes [Berdan-type]. With the exception of the aluminum cased "Blazer" ammunition previously mentioned, U.S. manufactured centerfire ammunition uses the Boxer type ignition system. Nearly all foreign ammunition, with the exception of that imported to the U.S. for sporting purposes, is Berdan primed. melcon s. lapina Primer Systems: Boxer & Berdan: The head of the cartridge is where the priming mixture is located either in the folded rim of a rimfire cartridge or in a small cup called a primer in centerfire cartridges. The head of a centerfire cartridge will have one of the following five ( 5) forms depending on the wishes of the original designer of the particular cartridge. Primer Systems: Boxer & Berdan melcon s. lapina Head Types: Head Types melcon s. lapina Slide163: Centerfire handgun cartridges specifically designed for use in revolvers will have a true rim. Examples are .32 S&W, .38 Special, .44 Magnum and .45 Long Colt. Centerfire handgun cartridges specifically designed for semiautomatic pistols are described as either being semi-rimmed or rimless even though they both have a rim. The distinction is based on whether the rim has a diameter greater than the adjacent case body. These distinctions are sufficiently large that, with a little practice, one can discern the difference between rimmed, semi-rimmed and rimless cartridges by visual inspection alone. melcon s. lapina Slide164: This matter of rimmed, semi-rimmed, rimless, rebated or belted cartridges relates to the means by which the unfired cartridges are properly positioned in the firing chamber of the gun for which they were intended. Some examples of how the common types of cartridges are chambered in revolvers, semiautomatic pistols and rifles are shown on the previous page. melcon s. lapina Cartridge Names: Cartridge Names The naming of cartridges, at least in the U.S, has not followed any precise rule. Because of the competitive nature of American industry and the large number of individuals engaged in hunting, target and recreational shooting as well as the law enforcement and personal defense markets, numerous systems and approaches have been used over the last century for naming new cartridges. melcon s. lapina Slide166: All cartridge names begin with some reference to nominal bullet diameter either in hundredths or thousandths of an inch or in millimeters. Until recently the U.S. and Britain have used decimal inches (examples: .45 Automatic and .303 British). More recently U.S. and British military cartridges and even some sporting or commercial cartridges of U.S. design have used the metric naming method (e.g., 5.56mm, 7.62mm NATO and 10mm Auto.) The original names for the first two examples are the 223 Remington and the .308 Winchester. melcon s. lapina Slide167: After some notation of nominal bullet diameter, additional descriptive information will follow which may relate to the cartridge's length (exclusive of the bullet), its design, the firm or individual that developed it, the loading, the year of adoption by the military or the muzzle velocity of the projectile. Example of each are given in the next slide. melcon s. lapina Slide168: melcon s. lapina Common CalibersInches & Metric Equivalents: Common Calibers Inches & Metric Equivalents melcon s. lapina Cartridge Types & How They Chamber in Firearms: Cartridge Types & How They Chamber in Firearms The chambering of a rimmed cartridge in the cylinder of a revolver. melcon s. lapina Slide171: The chambering of a .22 RIMFIRE (rimmed) cartridge in a rifle or autoloading pistol. melcon s. lapina Slide172: The seating of a true rimless cartridge suchas the 9mm Luger, .380 ACP or .45 ACP takes place against the square shoulder at the front end of the chamber and the case mouth (which must therefore, be left square and notcrimped). Since the rim is no larger in diameter than the body of the case, it cannot be used as a seating point as it is in rimmed or semirimmed cartridges. melcon s. lapina Slide173: Chambering in an autoloading pistol using a semi-rimmed cartridge such as the .25 ACP, .32 ACP or .38 ACP is effected at the rear of the chamber as shown below. melcon s. lapina Slide174: The proper seating of bottlenecked rifle cartridges of the three types (rimmed, rimless and belted) is shown below. melcon s. lapina Common Domestic and Foreign Headstamps on .22 Caliber Rim Fire Cartridges : Common Domestic and Foreign Headstamps on .22 Caliber Rim Fire Cartridges melcon s. lapina Slide176: Remington-Peters, Remington Arms Co., Bridgeport, CN [phased out after 1985]
Winchester-Western Div., Olin Corp. melcon s. lapina Slide177: Winchester-Western “Wildcat” [introduced ca. '73-'74]
Win.-Western, New Haven, CN [discontinued ca. '72] melcon s. lapina Slide178: Winchester Repeating Arms “Super Speed”, New Haven, CN [introduced ca. 1880-phased out ca. 1970]
Federal Cartridge Co., Minn., MN melcon s. lapina Slide179: Smith & Wesson Ammunition Co., Alton, IL [No longer mfgd.; nickel case=CDM-Mexico/brass case=Winchester]
CCI “Mini-Mag”, Cascade Cartridge, Inc. Lewiston, ID [introduced early 1960s, this headstamp discontinued ca. 1970] melcon s. lapina Slide180: CCI “Mini-Mag” [transition headstamp]
CCI “Mini-Mag” [current style - '91] melcon s. lapina Slide181: CIL, Dominion Ammunition Div. Montreal, Canada
“Valor” Precise Imports Co., Suffern, NY [mid 1970s import from Yugoslavia] Subsequently imported by the Hansen Cartridge Co., Southport, CN ca. 1983 melcon s. lapina Slide182: “Stirling” Squires Bingham Mfg., Marikina-Rizal, Philippines
Lapua Cartridge Factory, Lapua, Finland melcon s. lapina Slide183: Eley “Tenex”, Imperial Metals Industries (Kynoch) Ltd., Birmingham, England
Remington “Yellowjacket” [Introduced ca. 1980; headstamp changed to #17 in 1985] melcon s. lapina Slide184: Remington [Introduced in 1985; in use as of summer 1991]
“Seeker”, Altair Agencies, Inc. San Carlos, CA [mfgd. in the Philippines] melcon s. lapina Slide185: Sovereign “Tiger Cat”, Industrias Tecnos, Mexico
Pan Metal Corp. (PMC) [mfgd. In So. Korea, ca. 1988-present ('91)] melcon s. lapina Headstamps on Common CENTERFIRE Pistol and Revolver Cartridges: Headstamps on Common CENTERFIRE Pistol and Revolver Cartridges melcon s. lapina Slide187: Federal Cartridge Corp., Minneapolis, Minn.
Federal Cartridge Corp., Minn., MN.
Smith & Wesson-Fiocchi Inc., Alton, Illinois (discontinued ca. 1973) melcon s. lapina Slide188: Smith & Wesson Ammunition Co. Alton, IL
Winchester-Western Div., Olin Corp., Winchester Group, East Alton, IL
Same as above melcon s. lapina Slide189: Remington-Peters, Remington Arms Co., Bridgeport. CT [Note: the dash (-) was discontinued in 1971 and replaced with a dot (.) between the R and P]
Remington Arms Co., Bridgeport, CT [UMC=Union Metallic Cartridge; this headstamp was discontinued in 1961]
Remington Arms Co., Bridgeport, CT melcon s. lapina Slide190: Winchester-Western Div., Olin Corp., Winchester Group, East Alton, IL
Same as above
Winchester Repeating Arms Co., New Haven, CT melcon s. lapina Slide191: Remington heastamp since 1971
Patton & Morgan Co. (mfg. by Poongsan Metals Co., Seoul, Korea)
Speer-Omark Industries, Lewiston, ID melcon s. lapina Slide192: Super Vel (original co. in Shelbyville, IN; re-established in Fond-du-Lac, WI
Gulf+Western Systems Co., Waukesha, WI
Norma Projectilfabrik, Sweden melcon s. lapina Slide193: Hirtenberg Patronen, Hirtenberg, Austria
Svenska Metallverken, Stockholm, Sweden
Valor mfg. at Prvi Partizan factory, Yugo. melcon s. lapina Slide194: Typical U.S. Military headstamp: arsenal abbreviation and year of mfg. [Frankfort Arsenal – 1940]
Gustav Genschow Co., Berlin, W. Germany
Gevelot, Paris, France melcon s. lapina Slide195: Manurhin, Mulhouse, France
Cartuchos Deportivos de Mexico, Cuernavaca
Israeli Military Industries (“Samson”) Israel melcon s. lapina Slide196: CCI Blazer-Omark Industries, Lewiston, ID
RIO Brand – CBC, Brazil
Hornady Mfg. Co. – Grand Island, NE melcon s. lapina Small Arms Propellants(“Gunpowder”): Small Arms Propellants (“Gunpowder”) melcon s. lapina Black Gunpowder: Black Gunpowder The true origin of black gunpowder appears to be lost to antiquity. Its use in explosive and pyrotechnic devices predates the invention of firearms in the 1300's From the time of our revolution to the end of the 1800's it was the only propellant available for use in firearms. melcon s. lapina Slide199: Although it has been replaced by nitrocellulose based ("smokeless") propellants for nearly a century, it occasionally appears in shooting incidents largely because of the renewed interest in historic firearms (usually replicas of famous guns of the last century). Black powder and a relatively new (ca. 1978) black powder substitute called Pyrodex are manufactured for use in such guns. melcon s. lapina Slide200: Black gunpowder is a mechanical mixture of three (3) ingredients: potassium nitrate (KN03), charcoal (C) and sulfur (S) in an approximate ratio of 75:10:15 parts. Because of the water solubility of potassium nitrate, it is easily deactivated by moisture. It is spark sensitive and has an auto-ignition temperature of about 500 degrees F. melcon s. lapina Slide201: As a propellant in firearms and small cannons it is supplied in four granulations: Fg, FFg, FFFg and FFFFg with 4-F being the finest granulation. Except for the differences in particle size, unfired black gunpowder looks like shiny, irregular pieces of coal under the stereo microscope. Upon discharge it creates much smoke (particulate matter), a characteristic sulfurous odor and leaves considerable solid residues in the bore of the gun. The primary constituents of these solid residues are potassium carbonate and potassium sulfate and sulfides. melcon s. lapina Pyrodex : Pyrodex Pyrodex is presently offered in three (3) granulations for use in firearms: CTG for large caliber cartridges, RS for muzzleloading rifles and shotguns and P for percussion pistols. As with black powder the particle size effects burning rate during discharge. Pyrodex also contains potassium nitrate, charcoal and sulfur but in different ratios than black powder. melcon s. lapina Slide203: In addition, Pyrodex contains potassium perchlorate (KC 104), sodium benzoate and dicyandiamide (1cyanoguanidine) along with small amounts of dextrine, wax and graphite. The presence of these additional compounds permits various analytical methods to be used to differentiate Pyrodex residues from those of black gunpowder, e.g., high performance liquid chromatography, energy dispersive elemental analysis and/or FT-IR (infrared spectroscopy). melcon s. lapina Slide204: Prior to ignition Pyrodex is easy to differentiate from black powder. The granules appear as gray, globular particles with some non-homogeneous translucent areas in them. It is more difficult to ignite than black powder, has an auto-ignition temperature of about 750 degrees F and as a consequence is rated by the DOT as a class B flammable solid whereas black powder is classified as a class A explosive. melcon s. lapina Nitrocellulose Propellants : Nitrocellulose Propellants Nitrocellulose-based propellants were developed in Europe at the end of the 1800s. Due to their much-improved efficiency the term "smokeless" gunpowder has been applied to these propellants although there is still some smoke generated during their discharge. The basic ingredient in a single base smokeless gunpowder is nitrocellulose. This organic compound is made by the action of concentrated nitric acid on cotton or other source of cellulose fibers. melcon s. lapina Slide206: The purified nitrocellulose (NC) is gelatinized with various solvents and after the incorporation of selected additives and coatings, it is formed into very specific shapes and particle sizes. Some manufacturers have incorporated selected percentages of nitroglycerine (NG) into the nitrocellulose. Such propellants are called double base powders. Both types are much more efficient than black gunpowder or Pyrodex. They create higher internal pressures during discharge resulting in higher muzzle velocities for the projectiles and leave much less solid residues in the gun and fired cartridge cases. melcon s. lapina Physical Forms of Smokeless Powders: Physical Forms of Smokeless Powders While in a gelatinous state the NC or NC/NG mixture can be extruded through circular orifices of selected diameter to produce several common forms of smokeless gunpowder. If the extruded propellant is cut into relatively long pieces it is called tubular powder. After coating with graphite to improve their flow characteristics through powder metering devices and to dissipate static charges, the individual particles look like small pieces of pencil lead. melcon s. lapina Slide208: The tubular IMR (Improved Military Rifle) powders made in the U.S. have a central perforation down their long axis to modify the burning characteristics of the grains. Some tubular powders found in European ammunition lack this central perforation and may have their ends cut on an angle. The length and diameter of the individual grains of tubular powders is a useful class characteristic in comparing the powder in unfired cartridges. melcon s. lapina Slide209: Single base tubular powders such as the IMR series are typically used in centerfire rifle cartridges because of their relatively slow burning rates, the large powder capacity of centerfire rifle cartridges and the relatively long barrels of such guns. melcon s. lapina Slide210: Two more forms of smokeless powder are made by the extrusion process simply by cutting the sticks of powder into much shorter pieces so as to form wafers or discs. The thickness and diameter together with the presence or absence of a central perforation and the nature of various additives (which often includes NG), affects burning rate. Perforated and unperforated disc-flake powders burn faster than the tubular forms with similar chemical compositions. melcon s. lapina Slide211: Such propellants are commonly used in 22 rimfire ammunition, shotgun shells and centerfire pistol and revolver ammunition. Perforated and unperforated discflake powders with their graphite coatings look like gray wafers or flattened donuts when viewed under the stereomicroscope. melcon s. lapina Slide212: Another physical form of smokeless gunpowder is made by rolling the NC or NC/NG mixture into thin sheets of selected thickness and cutting it into square, diamond or parallelogram-shaped particles. These square-flake or Lamel forms of smokeless powder are presently all of foreign manufacture. Consequently they are frequently found in foreign ammunition. melcon s. lapina Slide213: Several Lamel-type powders have been imported into the U.S. by the Alcan Powder Co. of Sweden for use by handloaders of ammunition. The burning rate of these powders is controlled by size, thickness and additives. This form of propellant can be found in all types of ammunition (pistol, revolver, rifle, shotgun). melcon s. lapina Examples of Extruded Powders: Examples of Extruded Powders TUBULAR
(IMR 4831) PERFORMATED
(AL-120) NOTE: These examples are shown at approx. 6x melcon s. lapina Examples of Extruded Powders: Examples of Extruded Powders UNPERFORATED
LAMELS (AL-7) NOTE: These examples are shown at approx. 6x melcon s. lapina Ball Powders : Ball Powders In the early 1900's Dr. Fred Olson developed a new form of smokeless powder called ball powder (first commercially marketed by the Western Cartridge Co. in 1933). In this method the nitrocellulose is agitated and dispersed in a solution in which it is insoluble. The particles of NC form into tiny spheres (like an oil in water emulsion). melcon s. lapina Slide217: The size and shape of these particles are controlled and modified at various steps in the manufacturing process. Nitroglycerine may be added as well as other chemical coatings along with the usual graphite coating to the surface of the particles. melcon s. lapina Slide218: Burning rates are in part predicated on particle size. In a particular type of ball powder (Winchester 296 for example) there will be a range of diameters for the particles. Flattening of the spheres between rollers is also used to modify the internal ballistic performance of the propellant. melcon s. lapina Slide219: This flattening process can be so severe as to create a flat, flake-like particle that is almost unrecognizable as having once been a spherical powder particle. This highly modified form is called cracked ball by the industry. Irregular flake has also been used to describe this physical form of propellant but is less desirable in the writer's view. melcon s. lapina Slide220: Ball or spherical powder is also offered by the Hodgdon Powder Co. and it has also been found in foreign ammunition including some made in the Soviet Union.
In its pristine form the individual particles will be spherical. If they have been somewhat flattened between rollers then they would be classified as flattened ball powder particles. Examples of each of these three (3) forms of ball powder are shown on the next slide at the same order of magnification as those on the preceding slides. melcon s. lapina Slide221: Spherical Ball (H870) Flattened Ball (BL-C(2)) Cracked Ball (W-231) melcon s. lapina Forensic Elements of Gunpowder: Forensic Elements of Gunpowder The forensic value associated with gunpowders arises from the fact that no gun-ammunition combination is 100% efficient consequently some unburned and partially burned particles of propellant will be discharged from the muzzle. Where the distance between the muzzle of the gun and the victim or object are short (typically 2 to 3 feet or less) such powder particles may be deposited on the victim or the victim's clothing. melcon s. lapina Slide223: At very close ranges, powder particles are frequently driven into the skin. They can also leave a permanent pattern on inanimate objects and surfaces at such close ranges. Some of these unconsumed powder particles will usually be left in the bore of the gun and inside the fired cartridge case. They may, on occasion, even leave their imprint in the base of the fired bullet particularly when such bullet has an exposed lead base. melcon s. lapina Slide224: The physical form and/or chemical composition of powder deposits on a victim, an article of clothing or other object can be used to associate a particular firearm or type of ammunition with the shooting and exclude others. The sequence of shots can be established in some cases where mixed brands or loadings of ammunition have been used in the responsible gun. Muzzle distance determinations can be made from gunshot residue patterns around a gunshot wound or bullet hole when the responsible firearm and ammunition are available. melcon s. lapina Slide225: Revolvers offer an additional source of gunshot residue from the cylinder gap. Deposits produced at the cylinder gap and from the muzzle when revolvers are discharged alongside a surface provide distance and orientation information as well as an indication of the barrel length of the responsible gun. melcon s. lapina Firearms Discharge Patterns and Gunshot Residues: Firearms Discharge Patterns and Gunshot Residues Unburned powder particles only represent one aspect of firearms discharge products. Other materials emerge from the muzzle of a gun upon discharge. These include particles of bullet metal (either eroded away by friction and/or the hot powder gases driving the bullet down the bore), carbonaceous particles (soot) from the incomplete combustion of the propellant, bullet lubricant (when present on the bullet) and certain inorganic elements from the primer composition (primarily lead, barium and antimony in modern American centerfire ammunition). melcon s. lapina Slide227: Foreign ammunition and very old U.S. centerfire ammunition frequently have mercury and chlorine present in their primer mixtures (from mercury fulminate and potassium perchlorate). melcon s. lapina Slide228: The soot and primer residues are discharged as a very fine aerosol in the hot gas cloud that emerges from the muzzle at the moment of discharge. Because of their very low mass and small size, these finely divided particles quickly loose their velocity while the larger, heavier particles of partially consumed gunpowder for example will retain their velocity longer. The diagram and subsequent descriptions serve to illustrate how these materials will disperse and distribute themselves with increasing range. melcon s. lapina Gunshot Residue Production: Gunshot Residue Production melcon s. lapina Characteristics of GSR Deposits:: Characteristics of GSR Deposits: Muzzle Perpendicular to Receiving Surface melcon s. lapina Zone I: Contact: Zone I: Contact Blast destruction, tearing of the skin or clothing. Soot and powder particles mostly on the inside of the garment or driven into the wound. The outline of certain contacting parts of the firearm (e. g., front sight, barrel bushing) may be printed in the skin adjacent to the entry hole. melcon s. lapina Zone II: Near-Contact [ca. 1-4 inches]: Zone II: Near-Contact [ca. 1-4 inches] Intense, dark sooting with dense deposits of unburned and partially burned powder particles around the bullet hole. Blast destruction still possible in clothing and even skin in some cases. Powder tatooing on the skin. melcon s. lapina Zone III: [ca. 3-8 inches]: Zone III: [ca. 3-8 inches] Some medium to light gray sooting with a roughly circular "shotgun" pattern of powder particles around the bullet hole. Powder tatooing is still possible particularly with dense and/ or poorly burning powders. melcon s. lapina ZONE IV: ca. [6-36 INCHES] : ZONE IV: ca. [6-36 INCHES] No visible sooting. Widely dispersed powder particles often loosely adhering to the receiving surface. The distribution pattern is usually circular at closer distances but may become poorly defined to non-existent at greater distances. Chemical tests can be employed to raise latent powder or GSR patterns on garments. melcon s. lapina ZONE V: [ca. 3-4 FEET or GREATER] : ZONE V: [ca. 3-4 FEET or GREATER] No discernible firearms discharge products present. Bullet wiping present around the margin of the entry side of the bullet hole regardless of range. melcon s. lapina Slide236: Note: These descriptions are quite general. Specific gun and ammunition combinations may give markedly different results, e.g. ball powder from a short barreled gun may produce tatooing at several feet. melcon s. lapina Slide237: Gunshot residue deposits on skin, clothing or other surface will generally have a circular pattern or distribution around the bullet hole if the gun was discharged at a right angle to a relatively smooth, flat surface. The diameter of the circular deposits, the intensity of the soot (if any) and the density of the adhering powder particles are all related to the separation distance between the muzzle of the gun and the receiving surface. melcon s. lapina Slide238: It is this pattern that the firearms examiner attempts to recreate by test firing the gun at various known stand-off distances using ammunition of the same brand, type and propellant loading. Therefore careful handling and packaging of clothing or other objects bearing GSR deposits is of considerable importance if the distance between the gun and victim or object is in dispute or at issue. melcon s. lapina Slide239: Impounding or obtaining more of the same ammunition as that used in the shooting is also important since changing any of the parameters of brand, bullet type and weight or propellant loading could significantly alter the test results. It may even be desirable to ultimately use a portion of the actual clothing taken from a non-critical area to produce the final test patterns. melcon s. lapina Slide240: The close-proximity discharge of firearms substantially off of a perpendicular angle will produce an asymmetrical deposition of gunshot residues. These deposits will generally have a somewhat elliptical shape with a greater density of soot and/or powder deposits on the approach side. Holding a gun alongside a surface at the moment of discharge may also produce GSR deposits even though the bullet does not strike or perforate the surface receiving the deposits. melcon s. lapina Slide241: Revolvers fired in such orientations-offer special benefits to the forensic scientist. The location and intensity of the cylinder gap deposits and residues from the muzzle blast can be used to estimate the length of the barrel as well as the stand-off distance and orientation of the revolver at the moment of discharge [see the illustrations in the next slide]. melcon s. lapina Slide242: melcon s. lapina Slide243: Several terms have been used in these general descriptions of gunshot residue (GSR) deposits. Tatooing consists of powder particles which are embedded in and under the skin through the force of their impact. Tatooing is a close range phenomenon. When the range increases to the point that the powder particles lose the energy necessary to embed themselves in skin but still leave a visible defect or injury, the term stippling is often used. At close range unburned powder particles may produce stippling in inanimate objects such as wood, plastic, painted or varnished surfaces, plaster walls, etc. melcon s. lapina Slide244: The bearing surface of a fired bullet (even one fired through a clean gun barrel) will have powder and primer residues smudged on it as well as some galling or scuffing of the bullet metal itself from frictional forces during discharge. As the fired bullet forces its way through the first object it encounters much of this surface debris will be wiped off and deposited around the margin of the bullet hole. Thus the term bullet wipe. melcon s. lapina Slide245: Subsequent objects or surfaces struck and perforated (if any) will acquire much less if any bullet wipe around the bullet hole. Microchemical tests for traces of bullet metal (the dithiooxamide test for copper or the sodium rhodizonate test for lead) can be used to confirm any questionable hole as a bullet hole. Bullet lubricants with their own special characteristics may also comprise a portion of bullet wipe. melcon s. lapina Slide246: In the case of certain fabrics such as nylon and polyester, the impactive and frictional forces created during bullet passage through the garment will cause the partial melting of the severed fiber ends around the margin of the bullet hole. The birefringent properties of these fibers will also be changed. melcon s. lapina Slide247: Laboratory examination of the ends of such synthetic fibers with a polarizing microscope will allow these changes to be observed and may provide an alternate means of establishing a hole as a bullet hole. The forensic value of bullet wipe is to establish a hole as a bullet hole, to determine the entry side and on occasion, the sequence of shots or a bullet's passage through multiple objects. melcon s. lapina Gunshot Residue Tests - Summary: In summary, chemical and physical tests for various components of gunshot residue can be used to:
Detect the presence of latent (hidden) gunshot residues.
Verify any questioned deposits as GSR.
Verify any holes in garments or objects as bullet holes. Gunshot Residue Tests - Summary melcon s. lapina Slide249: Determine something about the bullet's composition (e.g., copper from a copper jacketed or plated bullet.)
Establish the type of propellant (where intact particles are found). These findings can be compared with the type of propellant residues in fired cartridge cases, the bore and chamber(s) of impounded guns and the propellant type in any unfired ammunition.
Establish the approximate range and on occasion, the orientation of the gun at the moment of discharge. melcon s. lapina Slide250: Where GSR patterns are present on skin or clothing and a distance determination is to be made, it is of critical importance to impound and submit to the firearms examiner ammunition of the same type along with the responsible gun. melcon s. lapina Slide251: One other phenomenon of forensic interest occurs during the discharge of a revolver. The leakage of gases and residues at the cylinder gap will leave a light to dark gray deposit around the face of the chamber from which the shot was fired. This halo or flare, although somewhat fragile and easily disturbed, is fairly conspicuous when viewed in proper light. melcon s. lapina Slide252: This is especially true if the gun has been cleaned or lightly oiled at some time prior to the discharge. Additional shots from other chambers will leave flares at each chamber opening often with an overlapping of the flare from a subsequent shot with that of a previous shot. melcon s. lapina Slide253: The presence of "fresh" (undisturbed, powdery gray) flares on the face of a revolver's cylinder allows one to state that the gun has been fired at least X times since the last cleaning (X=the number of flares). With a single shot from a revolver and no manipulation of the gun's mechanism afterwards, the singular "fresh" flare will be on the chamber under the hammer. If it is not under the hammer, it can reasonably be concluded that the gun's mechanism, particularly the cylinder, has been manipulated or rotated in some way after the shot was fired. melcon s. lapina Slide254: The presence, number and location of any flares on a revolver's cylinder may be important in an investigation to therefore the position of the cylinder in the gun at the time of recovery should be marked in some way prior to opening or removing the cylinder. melcon s. lapina Slide255: melcon s. lapina Chemical and Instrumental Methods in GSR Testing : Chemical and Instrumental Methods in GSR Testing melcon s. lapina Patterns/Residues on Surfaces: : Patterns/Residues on Surfaces: Close-proximity GSR deposits (soot/powder particles) on skin, light colored clothing or other light colored surface are usually visually apparent to the experienced observer. Deposits on skin should be adequately photographed. A scale of known units in the same plane as the visible residues should be included in some of the photographs in the event test patterns are to be made for a later estimate of the range of the shot. It would also be advisable for the medical examiner to collect a representative sample of the powder particles if present. melcon s. lapina Slide258: Clothing with visible gunshot residues should be carefully laid out on clean paper, allowed to dry if wet or bloody then rolled into a cylindrical package, sealed and marked. Latent (hidden) GSR deposits on dark or bloody clothing may be examined and tested by a number of methods. Infrared videography or photography will reveal carbonaceous soot and bullet wipe through a bloody background or on very dark garments. Soft x-rays can also be used to reveal powder particles and flecks of bullet metal. melcon s. lapina Slide259: Chemical transfer techniques such as the modified Griess test for nitrites using specially treated photographic paper will usually raise any powder pattern that may be present on the garment. The previously latent powder pattern will be transferred onto the paper lift as colored spots due to the reaction with nitrite residues in the partially consumed nitrocellulose. melcon s. lapina Slide260: Another technique -- the sodium rhodizonate test for lead deposits -- can be used in lieu of the modified Griess test or as an adjunct to the nitrite test. Depending on the color and condition of the garment, the rhodizonate test for lead may be applied directly to the garment or done with a lifting technique. melcon s. lapina Slide261: The lifting technique transfers a portion of any lead deposits or particles onto the special lifting paper where the lead residues are subsequently rendered visible as a pink adduct when the paper is sprayed with the sodium rhodizonate reagent. It should be noted that the lead that has been lifted from the garment has not been destroyed but merely transferred from one substrate to another and then complexed with the rhodizonate reagent. melcon s. lapina Slide262: It should also be pointed out that it is not necessary to have a lead bullet for there to be considerable lead deposits in gunshot residues. The primer mixture of nearly all modern ammunition contains lead styphnate (an impact sensitive explosive) and jacketed bullets possessing exposed lead bases will have a considerable amount of lead thermally eroded from their bases by the action of the hot powder gases during discharge. melcon s. lapina Slide263: Finally, the sodium rhodizonate test can also be used in many other applications in shooting investigations: to test possible bullet holes and/or ricochet marks in or on various surfaces, to test for lead "splash" or the impact of broken up bullet fragments and to raise lead-containing GSR deposits on items other than clothing. melcon s. lapina GSR Tests of the Hands of Subjects: GSR Tests of the Hands of Subjects The composition of contemporary priming mixtures was intentionally deferred until this section. It should be recalled that the priming mixture is the impact sensitive explosive mixture that is either distributed around the interior of the rim in a rimfire cartridge or located in the cup of a primer in a centerfire cartridge. In either case the impact of the firing pin detonates this mixture which in turn ignites the propellant charge. melcon s. lapina Slide265: The approximate compositions of three modern non-corrosive American centerfire primer mixtures are below. From a brief study of these formulations it should be noted that some form of lead styphnate, barium nitrate and antimony sulfide are common to all of them. The priming mixtures of centerfire ammunition from other countries however -- particularly military ammunition from the Soviet Union, Eastern Europe and mainland China -- often have very different compositions and frequently contain perchlorates and mercury fulminate. melcon s. lapina Some Representative Centerfire Primer Compositions of American Manufacture: Some Representative Centerfire Primer Compositions of American Manufacture melcon s. lapina Slide267: melcon s. lapina Slide268: Since the inorganic elements lead (Pb), barium (Ba) and antimony (Sb) in domestic centerfire ammunition are not consumed in the detonation of the primer mixture, they become apart of the discharge products the emerge from the muzzle of the gun in the form of very finely divided particles. melcon s. lapina Slide269: Two of these constituents (barium and antimony) when found in combination with each other are essentially unique to firearms discharges. The hands of a shooter or handler of a firearm many become contaminated with these materials. The hands of a victim may also bear elevated levels of these elements if, for example, the victim throws up his or her hands at the moment of discharge and they are in close proximity to the gun. melcon s. lapina Slide270: Several analytical techniques have been developed in the last 20 years to test hand swabbings for the presence and qualities of barium and antimony as well as lead where the first two are found. Such residues may also be collected by various lifting techniques (e.g.- tape lifts) and subsequently examined with a scanning electron microscope (SEM) equipped with an elemental analyzer. The physical appearance of primer residues under the SEM are very characteristic. They have a near-spherical, molten appearance and typically contain barium, antimony and lead upon analysis. melcon s. lapina Slide271: Both approaches (bulk analysis of hand swabbings or specific particle identification with lifting methods and SEM examination) are rather time consuming and expensive to carry out. Furthermore there are some important considerations relating to the passage of time and the actual composition of the evidence ammunition's priming mixture that stand to seriously affect the application or suitability of this type of testing. The passage of time and normal activities will gradually remove any GSR deposits that might be on the hands of the shooter. melcon s. lapina Slide272: Most laboratories that do this type of testing will set a cutoff time of four (4) hours from the incident to the apprehension of a suspect. Not all ammunition contains barium, antimony and lead. The table on the next page summarizes the status of commonly available .22 rimfire ammunition. melcon s. lapina Slide273: Several ammunition manufacturers are presently offering lead-free centerfire ammunition which also appear to lack barium and/or antimony in their composition. Finally, some guns are "dirtier" than other guns. In some cases the laboratory has found that a particular gun simply does not leave measurable GSR deposits on the hands of the person firing the gun. melcon s. lapina Marking Firearms and Firearms Evidence: Marking Firearms and Firearms Evidence melcon s. lapina Slide275: The following information and illustrations are suggestions for marking firearms evidence if it is deemed desirable to mark such evidence. Some agencies or laboratories may have strict protocols in this regard. Consequently the suggestions offered here may be superseded by such organizational policies. melcon s. lapina Slide276: The guiding principle should be to utilize a procedure that will allow you to later establish to the court's satisfaction that this is the item (gun, bullet, cartridge, wad, etc.) that was collected. In situations where an item cannot be reasonably marked (such as a small fragment of a bullet) such evidence should be secured in a suitable container, the container marked as to item number, date, time, finder, description, location found, etc., sealed and the seal marked in such a way that breaking of the seal would be discernible. melcon s. lapina Slide277: “It is desirable to cushion or wrap small items (bullets, bullet fragments, cartridge casings) in a piece of clean paper before inserting them into a vial or container. This will prevent the object from rattling around in the container and obviate the loss of any adhering trace evidence. Do not use cotton for this purpose” melcon s. lapina Slide278: Some agencies and individuals take the view that no firearms evidence will be marked directly. Rather, they require impounding such evidence in a suitably marked container as previously described. This approach is both workable and justified so long as each subsequent examiner of the contents of such containers documents the nature of the previous seal and opens the item in such a way that the finder's markings are not obliterated. The only exception this writer would take with such a approach would be firearms themselves. melcon s. lapina Slide279: Relying on a serial number alone can be risky particularly with old, foreign-made guns since instances of two guns of the same make and model bearing the same serial number have been encountered. Additionally, the "serial numbers" recorded by some crime scene technicians or police officers may not be the serial number but rather a recurring number used by a particular manufacturer (e.g.- Smith & Wesson frame numbers). melcon s. lapina Slide280: On the following slides are some suggested locations for marking revolvers, semiautomatic pistols with exposed barrels (e.g., the P.38) and semiautomatic pistols with barrels housed inside the slide. Identifying marks should be in one or more discrete locations (e.g., one the frame of a revolver under the cylinder). melcon s. lapina Slide281: Such marks should not seriously deface the firearm. A set of index marks should also be placed on the right and left top sides of the cylinder in a revolver before the cylinder is rotated, opened or removed from the gun. This is best accomplished with a permanent-type marking pen. melcon s. lapina Some Suggested Sites for Marking Handguns: Some Suggested Sites for Marking Handguns melcon s. lapina Slide283: melcon s. lapina Slide284: melcon s. lapina Slide285: Revolvers deserve special attention since the location and order of the fired cartridges may be very useful in reconstructing the sequence of shots and/or the nature of any manipulation of the gun after firing. The figure in the following slide illustrates how a simple diagram can be prepared depicting the orientation and sequence of cartridges in the cylinder of a revolver. melcon s. lapina Slide286: melcon s. lapina Slide287: melcon s. lapina Slide288: NOTE: When marking such items, consider the location of all class and individual characteristics that might be present as well as any trace evidence deposits. If in doubt, wrap the item in a tissue or clean piece of paper, secure and seal in a vial or other appropriate container and thoroughly mark the sealed container. melcon s. lapina Shotgun Evidence: Shotgun Evidence melcon s. lapina Slide290: Shotguns present special challenges to crime scene investigators, medical examiners and firearms examiners. This is largely due to the great variety and complexity of this type of ammunition compared to bulleted cartridges. melcon s. lapina Slide291: There are numerous types of wads, shot collars, buffering materials, many sizes and compositions of shot available in this type of ammunition. All of these items have important evidentiary value. They also have their own special ballistic properties that can play a vital role in establishing the distance from which the shot was fired and the location of the shooter at the moment of discharge. melcon s. lapina Slide292: One of the frustrating aspects of shotgun shootings is that it is very seldom possible to identify shot pellets as having been fired from a particular shotgun. There are rare exceptions to this statement when large shot (buckshot) loaded in old-style shotshells is used and the sides of the pellets rub against the bore of the gun during discharge. Expended shotshells on the other hand, can be matched back to the responsible gun using the same principles as described for bulleted cartridges, i.e., firing pin impression, breechface signature, etc. melcon s. lapina Shotgun Design and Nomenclature : Shotgun Design and Nomenclature Shotguns may be semiautomatic, pump action, lever action, bolt action or of break open design. The latter mechanism is used in single shot and double barreled guns. Double barreled guns are manufactured with their barrels side-by-side or over-and-under. Shotguns were developed for small game hunting (ducks, quail, rabbits, etc.) although special purpose loads are available for deer hunting (buckshot and solid slug loads), personal protection, law enforcement and military purposes. melcon s. lapina Slide294: For traditional small game hunting the shells are loaded with selected sizes of hardened spherical lead shot. The cartridges for shotguns are therefore called shotshells. The various sizes of shot were developed for different types of game. High flying geese for example require a larger size of shot than a rabbit that breaks from under foot. melcon s. lapina Slide295: The shot in a shotshell is fired through a smooth, unrifled bore. The size of the bore in shotguns is expressed in terms of gauge. The actual bore diameters for shotguns are given below. The four most common gauges are underlined. melcon s. lapina Slide296: melcon s. lapina Choke : Choke In addition to having smooth, unrifled bores, the muzzle of a shotgun barrel may contain some degree of constriction to it. This is called choke and its purpose is to control the spread of the shot after it leaves the barrel. This constriction is usually described as Full, Modified, Improved Cylinder or Cylinder choke with the last one being somewhat of a misnomer since it has no constriction. The following table for a 12 Ga. shotgun with a bore diameter of .730 inches should give the reader some idea of the amount of constriction involved. melcon s. lapina Slide298: melcon s. lapina Slide299: The amount of choke in a shotgun barrel is frequently stamped in the barrel of the gun, sometimes in a coded fashion, e.g., "F" = full choke. More expensive guns may have an adjustable choke affixed to the barrel. Since distance or range determinations in shotgun shootings are usually done by measuring the shot pattern at various ranges, it is important that adjustable chokes not be moved when handling and impounding such guns. melcon s. lapina The Effect of Choke on Shot Pattern : The Effect of Choke on Shot Pattern melcon s. lapina Shot Sizes and Shot Charges: Shot Sizes and Shot Charges Lead shot comes in two (2) basic types: "drop shot" and buckshot. Buckshot are comparatively large lead balls formed in molds. It has little or no hardeners alloyed with the lead. The smaller "drop" shot is formed by pouring molten lead alloy through perforated pans of selected size located at the top of a shot tower. The molten metal forms into spheres as it drops to a cushioning pool of water about 130 feet below. A mechanical sorting process follows this to separate the various sizes and reject out-of-round members. melcon s. lapina Slide302: Drop shot sizes have been given numerical values. The common sizes loaded in U. S.-manufactured shotshells range from #9 to #4. There are two intermediate sizes between the numbered shot sizes and buckshot. These are Air Rifle and BB which might be found in some shells intended for goose hunting. There are also some very small sized shot (#10, 11 and 12) which are not loaded in shotgun shells but are found in certain specially designed centerfire pistol and 22 rimfire cartridges intended for use on small pests, snake loads, etc. melcon s. lapina Slide303: From the foregoing it may be apparent that the diameter of shot pellets decreases as their numerical value increases, e.g., #9 shot is smaller than #4 shot. There is a simple formula for deriving the nominal diameter of shot sizes 1 through 12. If one subtracts the shot size from the number 17 and divides the result by 100, the value obtained will be the diameter of the shot in inches:
17 - SHOT SIZE/ 100 = DIAMETER (inches) melcon s. lapina Slide304: Because of the potential environmental hazards of lead contamination in heavy use waterfowling areas, American manufacturers have developed and presently offer a variety of shotshell loadings with steel shot. Steel shot is made by forming soft steel wire into spherical pellets of selected sizes. Although harder, steel shot is less dense than lead shot. A pellet of steel shot will weigh about 70% of the weight of the same size pellet of lead shot. melcon s. lapina Slide305: The following illustration shows the common, traditional American lead shot sizes in the upper figure and the newer steel shotsizes in the lower portion of the figure. The average weight per pellet in milligrams (grams for buckshot) measured by the author is given for the commonly available lead shot. The weight per pellet values for steel shot have been calculated from data taken from literature from the Federal Cartridge Co. of Anoka, MN. melcon s. lapina Lead Shot Sizes: Lead Shot Sizes melcon s. lapina Lead Shot Sizes: Lead Shot Sizes melcon s. lapina Steel Shot Sizes: Steel Shot Sizes melcon s. lapina Slide309: In addition to the basic composition of recovered shot (lead or steel), the size of the recovered pellets of shot is an important class characteristic. Since fired pellets (particularly lead shot) become somewhat deformed during discharge and almost invariably are deformed upon impact, their weight becomes a useful alternative means to determine size. melcon s. lapina Slide310: The manufacturers' marking on the sides of most shotshells includes the size of shot with which the shell was loaded. Other marking printed on most U.S. manufactured shotshells includes the charge of shot (in ounces) and a dram-equivalent value which relates to the powder charge in the shell. Examples of several styles of contemporary shotshells are illustrated on the next page. The several types of wads shown in these cartridges all serve the same purpose; namely, to seal off the powder gases from the shot charge and to drive the shot out the barrel. melcon s. lapina Two Styles of Contemporary Shotshells: Two Styles of Contemporary Shotshells melcon s. lapina Exterior Ballistic Properties : Exterior Ballistic Properties Many other forms of wads exist. Each has its own unique ballistic properties when the cartridge in which they are loaded is discharged. In addition to the wads and shot emerging from the shotgun, there will also be gunshot residue and partially burned powder particles just as with bulleted ammunition. All physical forms of smokeless powder with the exception of tubular powder are used in shotshells. melcon s. lapina Slide313: In many modern shotshells there is a granular plastic buffer material mixed with the shot to reduce the deformation of the soft lead spheres during discharge of the shell. These polyethylene or polypropylene particles are expelled from the muzzle along with the lead shot and also have short range ballistic properties that can be useful in close range shootings. melcon s. lapina Slide314: The charge of shot itself spreads out rapidly over distance. The size of the pattern at any point along the path of the discharge is largely controlled by choke. The total number of pellets in a particular loading of shell will be determined by the size (weight) of the pellets and the charge size. The tabulation below gives the approximate number of pellets per shell for lead shot sizes #2 through #9. The exact number will vary slightly depending on exact alloy content and slight variations in pellet diameter. melcon s. lapina Shot Pellets Per Shell: Shot Pellets Per Shell melcon s. lapina Slide316: The maximum range of lead shot can be approximated from the Journee formula. Journee was a French general and ballistician at the beginning of this century who worked out a simple formula for lead spheres. For lead shot fired at muzzle velocities on the order of 1200 to 1300 f/s Journee's formula states "the maximum range of lead shot in yards is equal to 2200 times the diameter of the shot in inches." The trajectories and maximum range values for most U.S. shot sizes are shown below. melcon s. lapina Shot Range : Shot Range melcon s. lapina Slide318: From the Journee table it can be seen that shotguns, particularly when loaded with the smaller sizes of shot, are very short range firearms compared to bullets from rifles which may travel more than a mile when fired at departure angles of 20 to 30 degrees. Such maximum range determinations are usually associated with issues of potential injury causation when someone is claimed to have discharged a shotgun in someone's direction but failed to strike them. melcon s. lapina Slide319: It is the short range ballistics of the shot, the wads, shot collars and any buffer material that is of great interest and value to the forensic scientist. The exterior ballistic behavior of all of these components can be studied, measured and utilized in casework if the gun and ammunition is available. The following illustration provides a profile view of an idealized shotgun discharge. melcon s. lapina Shotgun Discharge Profile: Shotgun Discharge Profile melcon s. lapina Slide321: At close ranges of a few feet or less the wads and much of the buffer material (if present) will follow the shot charge into the struck object or wound. The pellets in the shot charge will still be very close together resulting in a single, large entry hole or wound. During the first few feet of flight the petals on the one-piece type plastic wads will open as they encounter air resistance. This is illustrated in a remarkable high speed photograph from the Olin-Winchester firm showing the discharge of a 12 Ga. shotshell (3D.E.: 1-1/8 Oz.: #7 shot) at 18 inches from the muzzle of a full choke gun. melcon s. lapina Slide322: Wads of this general type are made by all U.S. manufacturers of shotshells and they all go through a cycle of opening, then reversing ends (due to air resistance and an aft center of gravity) and then quickly loosing velocity because of their light weight. Slide323: This opening and reversal cycle typically occurs in the first 3 to 4 feet of travel and has very important forensic value. At such close distances the shot charge is still en masse and will produce a single entry defect. The impact marks and/or impact orientation of this type of one-piece plastic wad can resolve distance determination questions of 1 foot vs. 2 or 3 feet range. melcon s. lapina Plastic Wad in Flight: Plastic Wad in Flight One-Piece 12 Gauge Plastic
Wad at 18 Inches from Muzzle melcon s. lapina Slide325: If a wad of the type shown in the illustration below strikes an individual while in orientation 2, one or more rectangular "slap" marks in the skin will be produced. Such marks can also be seen or detected in clothing. If leadshot was contained in the wad's cup, the sodium rhodizonate test for lead will often raise such "slap" marks. Terminal ballistic damage will usually be detectable in the bottom of the cup if it impacted in orientation 2. At orientations 3 and 4 there will be no "slap" marks and the impact damage to the wad will be on the side and base respectively. melcon s. lapina Wad Reversal in Flight: Wad Reversal in Flight melcon s. lapina Slide327: If no objects are struck by the wad or wads from a shotgun shell, they will loose their velocity quickly and fall to the ground at a fairly reproducible distance beyond the muzzle of the gun. The spread of the shot after discharge will occur in a predictable manner over distance as illustrated. melcon s. lapina Slide328: At any particular distance the pattern produced by the shot will be circular in nature when the gun is discharged toward a flat surface oriented at a right angle to the axis of the bore. The diameter of the minimum circle that will contain the shot pattern is, for the most part, controlled by the range and the choke of the gun, not gauge. The type of wads employed in the shell can also affect the size of the pattern. Gauge, shot size and shot charge determine the number of pellets in the pattern. The size of the shot also has some influence on pattern size. melcon s. lapina Slide329: If one keeps everything else the same (gun,choke, muzzle velocity, range and simply changes the shot size, the smaller shot will spread slightly faster than the larger, heavier shot. melcon s. lapina Shot Pattern vs. Range: Shot Pattern vs. Range melcon s. lapina Slide331: Shotgun discharges against flat surfaces at angles other than the 90 degrees perpendicular will produce an elliptical pattern. The minimum diameter of the ellipse (d) represents the pattern diameter at the range from which the shot was fired. The intercept angle of the shot's trajectory against the struck surface can be calculated by dividing the minimum diameter d by the major diameter D and determining the arcsin of this number. melcon s. lapina Shot Pattern at Angles Other than 90 Deg.: Shot Pattern at Angles Other than 90 Deg. Angled Shot Pattern melcon s. lapina Shotgun Summary: Shotgun Summary Although shot itself cannot normally be matched back to the responsible gun that fired it, many class characteristic comparisons can be made between the recovered components (shot, wads, shot collars, buffer material) and any live ammunition seized or a fired shell left at the scene. A fired shotshell can be associated with the responsible gun through firing pin impression and breechface signature just as with bulleted cartridges. melcon s. lapina Slide334: In "no gun" cases, the brand of the shell (and sometimes the shot loading) and the gauge of the gun can be established from the recovered wad(s). The size and composition of the pellets can be determined. If a complete pattern is present on a surface or object, the total pellet count can establish the charge of shot (e.g., 1 1/2 ounce vs 1 oz of #6 shot). melcon s. lapina Slide335: Many reconstructive opportunities are available in shotgun shootings due to the unique nature of the ammunition and the exterior ballistic properties of the discharged components. It should be recognized that this monograph is not all-inclusive. There are a number of other aspects of shotgun shootings that have not been covered simply due to the limitations of a monograph vs. a textbook. However, this shortcoming should only stimulate the person interested in such matters to make further inquiry into the multifaceted aspects of forensic firearms evidence. melcon s. lapina General Concluding Comments: General Concluding Comments melcon s. lapina Slide337: This presentation has provided some insight into the considerable variety that exists in firearms mechanisms, cartridges, bullet types, shotgun shells, propellants and other ammunition components. The generation, deposition and interpretive value of gunshot residues and some other trace evidence aspects of shooting investigations have been presented. melcon s. lapina Slide338: The special problems and unique opportunities associated with shootings involving shotguns were only briefly illustrated in the time and space available.
My goal has been twofold. First, it has been to help you think; to help you evaluate the issues in shooting incidents and to decide: melcon s. lapina Slide339: What are the important questions in this case?
What sort of testing can be done to confirm or refute the various explanations or theories as to what happened? melcon s. lapina Slide340: Secondly, it has been to lay the basic groundwork for the more fascinating and complicated matter of reconstructing shooting incidents. This is, in fact, the ultimate goal of the criminalist or forensic scientist. melcon s. lapina Slide341: The careless misuse or criminal use of firearms generates a great many evidential opportunities for the diligent and thoughtful investigator which are not found with other weapons or activities. This evidence, properly recognized and gathered and properly analyzed will often allow the accounts of witnesses and the account of the shooter to be tested and the event to be reconstructed. In this latter regard it may be possible to determine: melcon s. lapina Slide342: THE MANNER IN WHICH A FIREARM WAS DISCHARGED;
THE RANGE FROM WHICH A FIREARM WAS DISCHARGED;
THE POSITION OR ORIENTATION OF A FIREARM AT THE MOMENT OF DISCHARGE;
THE POSITION OF THE VICTIM AT THE MOMENT OF IMPACT; melcon s. lapina Slide343: THE NUMBER AND SEQUENCE OF SHOTS IN MULTIPLE DISCHARGESHOOTING INCIDENTS;
OTHER EXTERIOR AND/OR TERMINAL BALLISTIC EVENTS THAT MAY HOLD SPECIAL MEANING. melcon s. lapina