Rifled Weapons Forensic Science Newsletter William A. Cox, M.D., FCAP www.forensicjournals.com June 15, 2017 INTRODUCTION Rifled weapons include handguns, pistols and revolvers, and rifles. These are weapons in which spiral grooves have been cut into the length of the interior or bore of the barrel (Fig. 1).
Fig. 1. The above figure is the traditional rifling of a 9 mm handgun barrel. (en.wikipedia.org) Rifling consist of lands and grooves (Fig. 2). Fig. 2. This figure depicts lands and grooves of a rifled barrel. (bevfitchett.us) The lands grip the bullet as it passes down the barrel, giving the bullet a rotation, which has a gyroscopic effect that increases the stability of the bullet s trajectory and thus its accuracy (Fig. 3).
Fig. 3. This image denotes the spiraling effect induced by rifling and its contribution toward accuracy. This is analogous to a quarterback throwing a football with a tight spiral, which gives the football far greater accuracy. (hunter-ed.com) In contradistinction to rifled weapons, shotguns are smooth bored. This is because rifling in a shotgun barrel would cause the shot to disperse to quickly in a 360 degree arc. GENERAL INFORMATION Handguns and rifles are breech-loading firearms in which the cartridge is inserted or loaded into a chamber, which is integral to the rear portion of the barrel. The breech or chamber has a slightly greater diameter than the rest of the barrel. The missile fits snugly into the breech-chamber, but is too large to pass through the barrel without being squeezed. The barrel is grooved in a spiral fashion from the breech-chamber to the muzzle, with the friction between the squeezed missile and the ridges between the grooves (lands) imparting to the missile a spinning motion. Handguns and rifles are designed to fire one missile at a time when the trigger is pulled. Handguns cause over 50% of all homicides in the United States, being its most common cause, as it is for suicides. It is estimated there are approximately 700,000 gunshot wound victims in the United States each year, of which approximately 30,000 die. Handguns and rifles are classified by their mechanism of firing and their method of advancing a new round into firing position.
Handguns include the single-shot pistols, Derringers, revolvers and auto-loading pistols (automatics). 1. Single-shot pistol has one firing chamber, which is part of the barrel. The single-shot pistol must be loaded manually each time the pistol is to be fired (FIg. 4). Fig. 4. The above is an example of Stevens single shot pistols. (icollector.com) 2. Derringers are a form of a single-shot pistol, which has multiple barrels, each of which is loaded and fired separately. Typically, a Derringer has two barrels (Fig. 5).
Fig. 5, This is an example of a Derringer. (cheeperthandirt.com) 3. Revolvers have a rotating cylinder carrying a variable number of shells, which are brought into firing position, one by one, each time the trigger is pulled. Revolvers are subdivided into single-action (Fig. 6) and double-action revolvers (Fig. 7). In single-action revolvers, the hammer must be manually cocked each time the trigger is to be pulled and the gun fired. Cocking the hammer revolves the cylinder,
Fig. 6. The above image is that of a Colt single-action Army revolver. (en.wikipedia.org) aligning the chamber with the barrel and the firing pin pressure applied to the trigger then releases the hammer, discharging the firing pin. Fig. 7. The above revolver is an example of a very early double-action revolver. It is a LeMat revolver, which was invented by Jean Alexandre LeMat of New Orleans, which featured an unusual secondary 20 gauge smooth bore barrel capable of firing buckshot. It saw service with Confederate Army during the Civil War (1861-1865) and the Army of the Government of National Defense during the Franco-Prussian war. (en.wikipedia.org) In the double-action revolvers a continuous pressure on the trigger revolves the cylinder, aligns the chamber with the barrel, and cocks and then releases the hammer, firing the weapon. The cylinder of a revolver may rotate either clockwise, such as Colt revolvers, or counterclockwise, such as the Smith & Wesson revolvers. 4. Automatic pistol is an inappropriate designation for what is in reality a semiautomatic handgun. The saw called automatic pistol is an auto-loader in which the trigger must be pulled for every shot fired. Each time the gun is fired, gases propel the slide on the top of the gun backward. As the slide goes backward it ejects the spent cartridge casing and recooks the gun. As the slide springs forward it feeds a
new cartridge from the magazine into the firing chamber. Semiautomatics are divided into three categories: single-action, traditional double-action or double-action only. The determination of which category a semiautomatic pistol falls under is determined by whether the hammer must be cocked before a shot can be fired. 1. Single-action automatic pistol must be cocked by first operating the slide or bolt, or, if a round is already chambered, by cocking the hammer manually. The Colt M1911 is an example of this style of action (Fig. 8). Fig. 8. This is an image of a Remington made Colt M1911. (en.wikipedia.org) All single-action semiautomatic pistols exhibit this feature, and automatically cock the hammer when the slide is first racked to chamber a round. However, a round can also be manually inserted in the chamber with the slide locked back. 2. Traditional double-action semiautomatics, such as the 9 mm Beretta Model 92, can be fired either by cocking the hammer or by pulling the trigger. The trigger mechanism has features that both allow the trigger to be cocked and release the hammer/striker when fully pulled, or to merely lock the hammer/striker in the cocked position when it is pulled to the rear and the trigger is not depressed. Another example of the traditional double-action automatic is the Walther PPK (Fig. 9).
Fig. 9. The above is an example of the Walther PPK-L model. (en.wikipedia.org) 3. Double-action only automatics can only be fired by pulling the trigger. It is a design which either has no internal gear mechanism capable of holding the hammer or striker in the cocked position (semiautomatic), or has the entire hammer shrouded and/ or has the thumb spur machined off, preventing the user from cocking it. The purpose of the double-action only in a semiautomatic is mostly to avoid the change in trigger pull between the first and subsequent shots that one experiences in the traditional double-action. It also avoids the perceived danger of carrying a cocked single-action handgun or having to lower the hammer in a loaded chamber. An example of a doubleaction only pistol is the Sig Sauer P 229 (Fig. 10).
Fig. 10. This is an example of a Sig Sauer P 229. (sigsauer.com) Rifles are firearms designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves ( rifling ) cut into the barrel walls. The word rifle originally referred to this grooving, and a rifle was called a rifled gun. This rifling, as discussed above, implants a spin to the fired missile, impacting a spin around an axis corresponding to the orientation of the weapon. Once the missile leaves the barrel, this spin lends gyroscopic stability to the projectile and prevents tumbling (FIg. 3). This allows the use of aerodynamically efficient bullets, as opposed to the spherical balls used in muskets, which improves range and accuracy. This spin also contributes to the total kinetic energy released by the missile on its penetration of the target. Barrel length is immaterial in classifying a firearm as a rifle. In the United States, Federal Law requires rifles to have a minimum barrel length of 16 inches. Rifles are typically subdivided into single-shot, lever-action, bolt-action, pump-action, and auto-loading. 1. Single-shot rifles have a firing chamber which is integral with the barrel. The single-shot rifle can only hold a single round of ammunition, which must be manually loaded after each shot (Fig. 11).
Fig. 11. This is a single shot rifle called the Shiloh Sharps Model 1874 Hartford in. 50-90 Sharps. (en.wikipedia.org) Fig. 12. This is the model 1873 Trapdoor Springfield rifle. It was the first standardissue breech-loading rifle adopted by the United States Army. (en.wikipedia.org) The history of firearms began with single-shot designs, with many centuries passing before multi-shot repeater designs became common place. Single-shot designs are less complex than revolver or magazine-fed firearms. Single-shot designs are still produced by many manufactures, in both cartridge and non-cartridge varieties. Almost all of the early cartridge-fed rifles were single-shot designs, taking advantage of the strength and simplicity of single shot actions. An example of these early single-shot rifles is the trapdoor or Allin action used in early cartridge conversations of the 1863 Springfield muzzleloading rifles (Fig. 12). 2. Lever-action rifles have a lever, which is an extension of the trigger guard. After the rifle is fired, the lever is pulled down so the spent cartridge casing can be ejected; when the lever is moved back up, a new cartridge is inserted into the firing chamber, which is followed by the hammer being cocked. Once this sequence is done, the rifle is ready to be fired again. Most lever action firearms are rifles although lever- action shotgun and pistols have been made. One of the most well known lever-action
Fig. 13. This is an example of Winchester Model 1873 toggle-link action. (enwikipedia.org) rifles is the Winchester Model 1873 (Fig. 13). The Winchester Model 1873 is often referred to as The Gun that Won the West. It was manufactured from 1873 to 1923. It first chambered a.44-.40 cartridge, which was the first centerfire cartridge, which became very popular. Over 720,000 of the Model 1873 were made up to 1923. An example of a lever-action pistol is the Volcanic Pistol.41 cal 6 Barrel 1855/1857 (Fig. 14). The earliest successful repeating shotgun was the lever-action Winchester M1887, designed by John Browning in 1885 (Fig. 15).
Fig. 14. This is an example of a lever-action pistol, the Volcanic Pistol. (en.wikipedia.org) FIg. 15. This is a modern reproduction of the Winchester Model M1887 lever-action shotgun. (en.wikipedia.org) 3. Bolt-action rifles are one in which the firearm bolt is operated manually by opening and closing of the breech, barrel, with a small handle, which is typically on the right-hand side of the firearm. When a shot is fired, the bolt must be manually pulled back. In doing so the spent cartridge casing is ejected. A new cartridge Is placed in the breech. The bolt is then pushed forward sliding a new cartridge into the firing chamber. This is followed by the cocking of the firing pin. Most bolt-action firearms are rifles. There are some bolt-action shotguns as well as a few handguns. The earliest bolt-action rifle was the Dreyse needle gun, the design of which was submitted to the Prussian Army in 1836 (FIg. 16). The Zundnadelgewehr/Prussian Model 1841 was not the first bolt-action weapon to see combat as it was not fielded until 1864. The United States purchased 900 Greene rifles which saw service at the Battle of Antietam in 1862 during the American Civil War.
Fig. 16. This is the Dreyse Zundnadelgewehr/Prussian Model 1841. After the Dreyse needle gun was submitted to the Prussian Army, it was adopted for service in December 1840 as the Leichte Perscussions-Gewehr M 1841, which was later named Zundnadelgewehr M 1841 in 1855. (en.wikipedia.org) This weapon was ultimately considered to be too complicated for issue to soldiers and was replaced by the Springfield Model 1861, which was a conventional muzzle-loading rifle. Bolt-action shotguns, while uncommon, do exists. One of the best examples is a 12 gauge manufactured by Mossberg featuring a 3-round magazine, marketed in Australia just after changes to the gun laws in 1997 heavily restricted ownership and use of pump-action and semiautomatic shotguns. An example of a bolt-action shotgun is the single-shot.410 bore shotgun based on the SMLE Mk III rifle (Fig. 17). Fig. 17. This is the SMLE No. 1Mk III rifle. (Short Magazine Lee-Enfield Mk III). This rifle was use by Israeli female soldiers during the Arab Israeli conflict in 1948. (en.wikipedia.org)
4. Pump-action or slide-action rifle operates through a manual movement of a slide under and parallel to the barrel to open, extract and eject a cartridge, load another cartridge, and cock the firearm. Once fired, the slider is slid rearward by hand, the action of which ejects the expended cartridge. It is then reloaded by moving the slider (forend) forward. The first slide action patent was that of Alexander Bain of Britain in 1854. An example of a pump-action firearm is the Winchester Model 1912 12-gauge shotgun (Fig. 18). Fig. 18. This is the Winchester Model 1912 12-gauge pump-action shotgun. (en.wikipedia.org) The pump-action, when used in rifles is referred to as a slide-action or more commonly in the 19th century as a trombone-action. An example of a pump-action rifle is the Colt Lightning Carbine, which was manufactured from 1884 to 1904. It chambered a.44-.40 caliber bullet (Fig. 19). Fig. 19. The Colt Lightning pump-action rifle. (en.wikipedia.org) 5. Auto-loading or semiautomatic rifles, fires, extracts, ejects, reloads, and cocks the weapon with each pull of the trigger using the force of the gas pressure or recoil to operate the action. After each shot the trigger must be released and then pulled again to repeat the cycle. It must be remembered auto-loading or semiautomatic refiles fire a single bullet each time the trigger is pulled. In contrast to this, a fully automatic rifle continues to fire missiles as long as the trigger is pressed and there is ammunition left in the magazine. The first successful design of the semiautomatic rifle was that of Ferdinand Ritter von Mannlicher in 1885, which resulted in the production of the Model 85. Perhaps the most famous semiautomatic rifle was the M1
Garand used by the American Soldiers in World War II (Fig.20). Initially, the Axis powers had only bolt-action weapons and only a limited number of semi-automatic rifles. Fig. 20. This is the M1 Garand, designed by John Garand in 1936 and was initially produced for the United States Military. (en.wikipedia.org) 6. Automatic rifle is a magazine-fed rifle that uses either its recoil or a portion of the gas propelling the missile to remove the spent cartridge case, cock the rifle, load a new cartridge and fire again repeatedly, as long as the trigger is held down or until the magazine is empty. As stated above, the automatic rifles differ from semiautomatic rifles in their ability to fire more than one shot in succession once the trigger is pulled. Many automatic rifles can fire in fully automatic or semiautomatic modes. The first automatic rifle was the Italian Cei-Rigotti introduced in 1900. The Browning automatic rifle (BAR) was one of the first practical automatic rifles (Fig. 21). The BAR made its successful combat debut in World War I. Approximately 50,000 were made before the war came to an end.
Fig. 21. This is the M1918A2 Browning Automatic Rifle. (en.wikipedia.org) CALIBER The caliber of a rifle or handgun, is either the internal diameter of the bore of the barrel before the rifling grooves were cut, measuring from land to land (Fig. 2) or the diameter of the bullet. Common caliber designations are given in either the English system in hundredths of an inch, i.e.,.22,.38,.45 or in the metric system in millimeters, i.e., 7.42 or 9 mm. Thus, a.22-caliber gun fires a.22-caliber bullet. Making certain the caliber of the bullet matches the caliber of the inner diameter of the barrel of the gun is essential because the bullet must maintain a tight fit with the inner barrel lining as the expanding gases accelerate it down the barrel of the gun giving it the proper rotatory gyroscopic effect and thus accuracy (Fig. 3). In the autopsy reports of Forensic Pathologist, they often describe bullets as small (.22,.25), medium (.32,.38, and 9 mm), or large (.40,.45,.50) caliber, which is based on the measurement of the bullet s diameter. It is important to understand, the caliber designation as used in the United States can be confusing for it is neither accurate or consistent. For example, the.303 Savage fires a.308-inch-diameter bullet. The.303 British cartridge has a 0.312-inch-diameter bullet. Both the.30-06 and the.308 Winchester cartridges are loaded with bullets having a diameter of 0.308 inches. The 06 in the.30-06 refers to the year of adoption of this cartridge. The European system of cartridge designation, which uses the metric system, is more thorough and logical than the US system. It identifies a cartridge by giving the bullet diameter and the case length in millimeters, as well as designating the type of cartridge case. Thus, the Russian rimmed service round becomes the 7.62 x 54 mmr. The 7.62 refers to the diameter of the bullet; 54 mm indicates the length of the cartridge case and R indicates the round is rimmed (Fig. 22). The.30-06 defined metrically would be 7.62 x 63 mm.
Fig. 22. The above shows examples of 7.62 x 54 mmr ammunition. Reading from left to right: Sellier & Bellot hollow point boat tail; Czech silver tip, mild steel core, light ball; Hungarian silver/yellow-tip, mild steel core, heavy ball; Wolf Ammunition Gold soft-point; USSR 1986 steel core light ball, Factory 60. [1]; Yugoslav surplus (1953); USSR 1940s lead core light ball [2]. The 7.62 x 54 mmr cartridge was developed by the Russian Empire and introduced as a service cartridge in 1891. Originally designed for the bolt-action Mosin-Nagant rifle it was used during the late Tsarist era and throughout the Soviet period to the present day. (en.wikipedia.org) ANOTHER FORM OF IDENTIFICATION OF BULLETS In addition to bullets being identified by their caliber or diameter, they are also identified as to whether they have a metal covering or jacketing. Metal jacketing increases the penetration of a bullet as it enters its target and permits the more efficient chambering of a cartridge (Fig. 23).
Fig. 23. These are examples of full metal jackets (FMJ) bullets in their usual shapes: pointed ( spitzer ) loaded in the 7.62 x 39 mm rifle and round-nosed loaded in the 7.62 x 25 mm pistol cartridges. (en.wikipedia.org) Jacketed bullets have a lead or steel core covered by an outside jacket of gilding metal (copper or zinc), gilding metal-clad steel, cupro-nickel (copper & nickel), or aluminum. The thickness of the jacket ranges from 00165 to 0.030 inches. Jacketed bullets may be either full metal-jacketed (Fig. 23) or partial metal-jacketed (Fig. 24). Fig. 24. This is a bullet with an exposed lead point. It is sometimes referred to as a partial metal-jacketed bullet. Unlike a full metal jacket that completely encases the bullet in a coating of metal alloy, the soft point leaves a portion exposed. (concealednation.org) Originally, all ammunition intended for automatic pistols was full metal-jacketed (FMJ).
FMJ bullets are used in the military to improve feeding characteristics. The harder gilding was less prone to deformation than softer exposed lead. FMJ also allows for higher muzzle velocities, thus they are used in high-velocity rifles. Full metal jacketed bullets completely encloses the tip of the bullet, preventing it from expanding when it reaches its target (Fig. 23). The tip of the bullet may either be pointed or rounded (Figs. 23 & 24). Remember, in full metal jacketed bullets the core may be exposed at the base (Fig. 25). Fig. 25. These are.30-caliber (7.62 mm) full metal jacket bullets, which show the typical jacket openings exposing the lead allow core on the base of the bullet to illustrate a full metal jacket may not completely enclose the core. (en.wikipedia.org) Jacketed bullets are used in high-velocity rifles to prevent the core from fragmenting or melting. Typically, rifles have a muzzle velocity, which varies between 1850 ft/sec to 3450 ft/sec. High-velocity rifles have a muzzle velocity, which varies between 3,500 ft/ sec (1,067 m/s) and 5,000 ft/sec (1,524 m/s). Hyper-velocity rifles have a muzzle velocity which exceeds 5,000 ft/sec (1,524 m/s)
Handguns have a muzzle velocity which varies between 650 ft/sec and 2200 ft/sec. Partial metal jacketing (FIg. 24) are typically soft-pointed rifle or pistol bullets with a lead core that is generally closed at the base. The lead core is exposed at the tip so as to facilitate expansion when the bullet strikes its target. The tip of the soft-pointed bullet may either be tapered to a point or have a rounded blunt end. WOUND BALLISTICS The total kinetic energy of a missile is due to two factors: Rotational or angular kinetic energy and the energy due to linear or translational motion. In essence, the total kinetic energy of a missile is the sum of its rotational kinetic energy about the center of its mass and the linear kinetic energy of the center of its mass. 1. Rotational or angular kinetic energy is the kinetic energy produced by a missile due to its rotation about the center of its mass. It is expressed by the following formula: KErotational = 1 Iw 2 2 In this formula w represents angular velocity and I represents rotational inertia (moment of inertia). 2. Linerar or translational motion is the kinetic energy a missile acquires during its acceleration from being motionless in the breech to its normal velocity. The missile maintains this kinetic energy until its speed changes. This kinetic energy is released into the body as the missile comes to a rest. Linear or translational kinetic energy is expressed by the following formula: KElinear = 1mv 2 In this formula m represents the mass of the missile and v represents its velocity. As can be seen in the above formulas, I in the rotating system, takes the place of m in the linear system, and the angular velocity, w, takes the place of the linear velocity, v in the linear system. The total kinetic energy of a missile is thus the sum of the rotational energy about the center of the mass of the missile and the linear kinetic energy of the mass of the missile. Wound ballistics and tissue damage will be discussed in a subsequent article. 2