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Glossary of firearms terms


Cast Iron
Oct 22, 2010
Central Valley, CA
Glossary of firearms terms

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All glossary terms are from the AFTE glossary, the SAAMI glossary, Encyclopedia Brittanica, or are supplied from subject matter experts unless stated otherwise.
· A
o Abrasion marks - See Toolmark, Striated
o Abrasive machining - The use of abrasives rather than high-speed steel or tungsten carbide cutting tools.
o Acetic acid - Chemical reagent used in Griess (Walker) test for gunpowder residue detection. Acetic acid forms nitrous acid in reacting with nitrites in gunpowder residues.
o Action - The working mechanism of a firearm. May be broken down into action types as follow.
§ Automatic – A firearm design that feeds cartridges, fires, extracts and ejects cartridge cases as long as the trigger is fully depressed and there are cartridges in the feed system. Also called FULL AUTO and MACHINE GUN.
§ Bolt – A firearm in which the breech closure:
§ (1) Is in line with the bore at all times.
§ (2) Manually reciprocates to load, unload, and cock.
§ (3) Is locked in place by breech bolt lugs and
engaging abutments usually in the receiver. There are two principal types of bolt actions: the turn bolt and the straight pull.
§ Box lock – A design in which the hammer and hammer springs are located within the frame and the trigger assembly in the lower tang. Generally found on double-barrel shotguns, such as Parker, Fox, Stevens, Winchester Models 21 and 24, etc.
§ Falling block – A single shot lever action mechanism. The breechblock slides vertically or nearly vertically, when the lever is moved, to expose or lock the breech. Example: Ruger No. 1.
§ Hinged frame – A design wherein the barrel(s) is pivoted on the frame. When the action is open, the barrel may pivot up, down, or sideways for loading or unloading. When the action is closed, the breech of the barrel(s) swings against the standing breech. Opening is normally accomplished by movement of a top-, side-, or under-lever.
§ Lever – A design wherein the breech mechanism is cycled by an external lever generally below the receiver.
§ Martini– A hammerless single shot rifle action, lever operated, in which the movement of the breechblock is entirely within the receiver and pivots at the rear.
§ Revolver – A firearm, usually a handgun, with a cylinder having several chambers so arranged as to rotate around an axis and be discharged successively by the same firing mechanism.
§ Rolling block – A single shot action in which a breechblock and hammer each rotate about their separate transverse pins in the receiver. The two members are swung rearward, away from the barrel breech to load the mechanism, or extract a cartridge case. To fire a cartridge, the breechblock is closed and locking is accomplished by the falling hammer engaging an abutment on the breechblock. Example: Remington No. 4.
§ Semiautomatic – A repeating firearm requiring a separate pull of the trigger for each shot fired, and which uses the energy of discharge to perform a portion of the operating or firing cycle (usually the loading portion).
§ Sidelock – A design in which the firing mechanism is attached to a sideplate rather than being integral with the frame.
§ Slide – An action which features a movable forearm which is manually actuated in motion parallel to the barrel by the shooter. Forearm motion is transmitted to a breech bolt assembly which performs all the functions of the firing cycle assigned to it by the design. Also known as PUMP ACTION.
§ Trap door – An action in which a top hinged breechblock pivots up and forward to open. Locking on this action is accomplished by a cam located at the rear of the breechblock that fits into a mating recess. Also known as a CAM LOCK.
o Action, turnbolt - A bolt action firearm on which it is necessary to rotate the bolt handle upwards for unlocking before it can be pulled to the rear. Similarly, it is necessary to rotate the bolt handle downward after closing to lock the firearm and enable the gun to be fired.
o Action marks - Abrasion or scratches placed on a cartridge case or bullet through the mechanical function of loading or unloading a cartridge or pistol.
o Adapters - See Subcaliber device
o AFTE Theory of Identification as it Relates to Toolmarks - 1. The theory of identification as it pertains to the comparison of toolmarks enables opinions of common origin to be made when the unique surface contours of two toolmarks are in "sufficient agreement."
2. This "sufficient agreement" is related to the significant duplication of random toolmarks as evidenced by the correspondence of a pattern or combination of patterns of surface contours. Significance is determined by the comparative examination of two or more sets of surface contour patterns comprised of individual peaks, ridges, and furrows. Specifically, the relative height or depth, width, curvature, and spatial relationship of the individual peaks, ridges, and furrows within one set of surface contours are defined and compared to the corresponding features in the second set of surface contours. Agreement is significant when it exceeds the best agreement demonstrated between toolmarks known to have been produced by the same tool. The statement that "sufficient agreement" exists between two toolmarks means that the likelihood another tool could have made the mark is so remote as to be considered a practical impossibility.
3. Currently the interpretation of individualization/identification is subjective in nature, founded on scientific principles and based on the examiner's training and experience.
o Age hardening - Hardening with time by precipitation.
o Aggregate ball - A variant of ball propellant seldom encountered today, formerly used as a shotshell propellant. They are so named because each “apparent” granule is an aggregate of smaller balls. The size of these subparticles can vary by a factor of ten.
o Ammunition, ball - One or more loaded cartridges consisting of a primed case, propellant, and with one or more projectiles. Also referred to as Fixed or Live Ammunition.
o Anvil - 1. An internal metal component in a boxer primer assembly against which the priming mixture is crushed by the firing pin blow. See Primer.
2. A metal feature in the primer pocket of a Berdan-primed cartridge case, against which the priming compound is crushed by the firing pin blow.
3. The breech end of the chamber in a rimfire firearm.
o Anvil marks - A term generally used by the military for a cartridge with a full metal jacketed bullet or solid metal projectile.
o Armor piercing bullets - See Bullet, Armor piercing.
o Associative evidence - Associative evidence can be used to provide links between evidence and individuals involved in a crime. In some cases, the associative evidence may be sufficient to prove the contact; in other cases, the associative evidence may be less definitive and provide corroboration of other evidence.
o Automatic - See Action, Automatic
o Azo dye - A result of the Griess test in which nitrites from gunpowder residues are converted to an orange-red dye.
· B
o Backspatter - See Bullet splash.
o Ball powders - See Powder, Ball.
o Ballistite - Trademark, applied to smokeless powder made of nitrocellulose dissolved in nitroglycerin (first made in 1888 and credited to Alfred B. Nobel, a Swedish chemist).
o Barrel blanks - An unfinished barrel in any state of completion.
o Barrel extension - A metal projection which extends rearward from the breech end of barrel into which the breech locks while the firearm is in battery or firing position. Example: Remington, Model 870.
o Barrel swaging - The process of forming the interior and/or exterior shape of the barrel of a firearm by hammering. Also called HAMMER FORGING.
o Barrel vent - An opening or series of openings in a barrel, normally near the muzzle, through which gases pass prior to bullet exit.
o Battery cup - A flanged metallic cup used in shotshell primer assemblies that provides a rigid support for the primer cup and anvil. Also called BATTERY POCKET.
o Bearing surface - That portion of a bullet’s outer surface that comes into direct contact with the interior surface of the barrel.
o Bench block - Usually hardened steel that has been worked and altered to serve a particular purpose. The gunsmith’s block has holes and channels cut into it that facilitate the disassembly of a firearm when used in conjunction with drifts and hammers.
o Bird shot - See Shot, Bird
o Black powder - See Powder, Black
o Blanking - Cutting or pressing a piece of metal from a sheet. Imagine an office hole punch made to handle steel metal. In ammunition manufacture, the usable part of a blanking operation is the material removed from the hole, usually a disk.
o Blowback - 1. In firearms, an automatic or semiautomatic firearm design that directly utilizes the breech pressure exerted on the head of the cartridge case to actuate the mechanism.
2. In ammunition, a leakage of gas rearward between the case and the chamber wall from the mouth of the case. See also Blowback, delayed
o Blowback, delayed - A system in which the breechblock is not locked but some mechanical delay is incorporated to ensure that the breechblock cannot move back with sufficient rapidity to allow the unsupported case to emerge from the chamber while the pressure is still high. Also known as RETARDED BLOWBACK.
o Blowby - 1. The escaping of gases past the bullet, while the bullet is in the barrel.
2. A slang term for "Blowback."
o Bolt - That portion of a lock which is moved into a locked or unlocked position, mechanically or electrically.
See also:
1. See Breech bolt
2. See Cylinder stop
3. See Latch
o Bolt action - See Action, bolt
o Bolt face - See Breech face
o Bore diameter - 1. Rifled barrels; the minor diameter of a barrel which is the diameter of a circle formed by the tops of the lands.
2. Shotguns: the interior dimensions of the barrel forward of the chamber but behind the choke.
o Boring - Producing smooth and accurate holes in a workpiece by enlarging existing holes with a bore, which may bear a single cutting tip of steel, cemented carbide, or diamond or may be a small grinding wheel.
o Borescope - An instrument for examining the bore and chamber of a firearm. It usually consists of a tube, mirror, light source, and the lens that can be inserted into the chamber or muzzle.
o Bottleneck cartridge - See Cartridge, bottleneck
o Box magazine - A rectangular receptacle attached to or inserted into a firearm that holds cartridges stacked on top of one another ready for feeding into the chamber.
o Bracketing - This is a technique to ensure correct exposure of photographs. This is achieved by taking two additional photographs – one slightly underexposed and another slightly overexposed.
o Breech face - That part of the breechblock or breech bolt which is against the head of the cartridge case or shotshell during firing.
o Breech-face marks - Marks characteristic of the breech under the firing pin and have been used to identify a cartridge case with a specific firearm. That part of the breechblock or breech bolt which is against the head of the cartridge case or shotshell during firing.
o Breech bolt - The locking and cartridge head support mechanism of a firearm that operates in line with the axis of the bore.
o Breech loading - A breech-loading weapon is a firearm (a rifle, a gun etc.) in which the bullet or shell is inserted or loaded at the rear of the barrel, or breech; the opposite of muzzle loading.
o Breechblock - The locking and cartridge head support mechanism of a firearm that does not operate in line with the axis of the bore.
o Breech-face markings - Negative impression of the breech face of the firearm found on the head of the cartridge case and/or primer after firing. Also see Matrix
o Broaching - Finishing surfaces by drawing or pushing a cutter called a broach entirely over and past the surface. A broach has a series of cutting teeth arranged in a row or rows, graduated in height from the teeth that cut first to those that cut last.
o Buckshot - Lead pellets ranging in size from .20” to .36” diameter normally loaded in shotshells.
o Bulk propellants - "Noncanister" propellants are sold in bulk to ammo manufacturers who have pressure testing equipment. Courtesy of Speer Glossary
o Bullet, armor piercing - 1. A bullet consisting of a hardened core or wholly composed of a substance other than lead or lead alloy.
2. Any bullet manufactured, represented, or designed to be metal or armor piercing.
o Bullet, boattail - A specific design of bullet having a tapered or a truncated conical base.
o Bullet, Brass washed - A term used for lead bullets with a brass-colored coating. Sometimes referred to as GOLDEN BULLETS. This coating has been used on 22 rimfires by manufacturers in the USA, Australia, Mexico, Austria, and the Philippines.
o Bullet, capped - Consists of a standard lead bullet having a harder metal jacket (gliding metal, copper, etc.) over the nose. Also known as METAL POINT BULLET.
o Bullet, cast - A bullet formed by pouring molten lead into a mold.
o Bullet, coated - Lead alloy bullet having a thin metal alloy coating. Examples: R/P “Golden Bullet” and W/W “Lubaloy.”
o Bullet, conoidal - A cone-shaped bullet. Also known as a conical bullet.
o Bullet, copper jacketed - A bullet having an outer jacket of copper or copper alloy and containing a lead alloy core.
o Bullet, copper washed - A term used for lead bullets with a copper-colored coating. This finish is found extensively on 22 rimfire cartridges from manufacturers around the world.
o Bullet, disintegrating - See Bullet, frangible.
o Bullet, dumdum - An obsolete term referring to an expanding bullet manufactured at the British Arsenal in Dumdum, India.
o Bullet, expanding - See Bullet, mushroom
o Bullet, exploding - A bullet containing a primer or other explosive and designed to explode upon impact.
o Bullet, flat-nosed - A bullet with flattened tip at right angles to its axis. See Meplat
o Bullet, frangible - A projectile designed to disintegrate upon impact with a hard surface in order to minimize ricochet.
o Bullet, full metal case - See Bullet, Full metal

From: Glossary
Courtesy of Gunsmith Services Main