Rifled Weapons-Forensic Science Newsletter-June 2017
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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 double- action 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 standard- issue 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.