Gunsmith Glossary

Gunsmith Glossary
ACCURIZE (accurizing): The process of altering a stock firearm to improve its accuracy.
ACTION: The physical mechanism that manipulates cartridges and/or seals the breech. The term refers to the method in which cartridges are loaded, locked, and extracted from the mechanism. Actions are generally categorized by the type of mechanism used. Action is not present on muzzleloaders because all loading is done by hand. The mechanism that fires a muzzle-loader is called the lock. Typically, firearms are single-action and double-action. Single-action uses manually cocked hammer, while double-action operation automatically cocks and releases the hammer by way of the trigger [two-stage operation]. 
ACTION, AUTOMATIC:  Type of firearm that delivers continuous loading, firing, and cartridge ejection while the trigger is depressed. Machine guns employ automatic action. Possession of automatic firearms by civilians requires special permission and licensing via the Department of Treasury, ATF Department. 
ACTION, BOLT:  Type of firing action that requires manual loading [or a small capacity magazine], manual hammer-cocking, and unloading. Unloading and loading is performed by retracting the bolt mechanism, which ejects the used cartridge and allows for the insertion of another. Bolt action rifles deliver good accuracy, which makes them popular for hunting, competition sports, and military snipers. 
ACTION, LEVER: Similar to bolt action, this mechanism uses an external lever, placed directly below the receiver to load new cartridges, cock the hammer, and unload spent cartridges. Several models of rifles use lever action, as well as Old West shotguns like reproductions produced by Uberti.  
ACTION, PUMP: This firing mechanism employs a sliding firearm that with a single pump chambers a new round and ejects the spent round. Once the forearm has been pumped, no cocking is required for the next discharge. Some models of shotguns are pump action.
ACTION, SEMI-AUTOMATIC: A firearm mechanism used on self-loading firearms that delivers a complete firing cycle that includes loading, firing, and discharging of the spent cartridge with each depression of the trigger.

BACK BORE or BACKBORED BARREL: A shotgun barrel whose internal diameter is greater than normal for the gauge. This is done to reduce recoil, improve pattern, or change the balance of the shotgun. 
BACKSTOP: The barrier behind the target at the range that stops bullets. The area shoud be free of debris, especially rock and metal to prevent ricochets. 
BALLISTICS: Scientific field dedicated to the physics of projectile launch and projectiles in motion. Interior ballistics focuses on movement inside the firearm; exterior ballistics focuses on movement through the air; and terminal ballistics focuses on movement through the target. Ballistic-expert forensic scientists use their knowledge to match bullets and cartridges with the "signatures" of individual firearms.  
BANDOLIER or BANDOLEER: A pocketed belt for holding ammunition cartridges, usually slung over the shoulder and across the chest. Bandoliers can still be found, but magazines have made them obsolete and are only used with shotguns to carry shells.
BARREL: A metal tube through which a controlled explosion or rapid expansion of gases are released in order to propel a projectile out at the end at high velocity.
BALLISTIC COEFFICIENT or BC: A measure of projectiles ability to overcome air resistance in flight. BC is a function of mass, diameter, and drag coefficient. In bullets it refers to the amount of drop over distance and wind drift that affects the bullet. 
BENCHREST:  A specialized, stable stand, platform, or table used by a shooter to support the limbs and body and steady the aim. Commonly used for sighting in a firearm and testing accuracy. Benchrests are also used in competition shooting events. 
BIG BORE: Generally a term used to refer to ammunition for handguns that are higher than .38 caliber and rifles .30 caliber and higher. In the United Kingdom it refers to rifles with .40 caliber and higher. 
BIRDSHOT:  Type of shotgun shot loaded into shotshells that consists of small pellets [less than .10 inches in diameter] made from lead or steel. This shot is intended for hunting bird and small game. 
BLACKPOWDER [GUNPOWDER]: A mixture of sulfur, charcoal, and potassium nitrate. It burns rapidly, produces a volume of gas that is carbon dioxide, water, and hydrogen with a residue of potassium sulfide. It is used in firearms, pyrotechnics, and various explosive devices. Modern firearms used smokeless powder that burns cleaner and with less smoke.
BLOWBACK: A system of operation for self-loading firearms that obtains power from the motion of the cartridge case as it is pushed to the rear by expanding gases created by the ignition of the powder charge.
BLUING or BLUEING: A passivation process in which steel is partially protected against rust, and is named for the blue-black appearance of the resulting protective finish. [See Parkerizing] True gun bluing is an electrochemical conversion coating from an oxidizing chemical reactions with iron on the surface selectively forming magnetite (Fe3O4), the black oxide of iron. Black oxide provides minimal protection against corrosion, unless also treated with a water-displacing oil [Break-Free] to reduce wetting and galvanic action. “Cold” bluing is generally a selenium dioxide based compound that colors steel black, or more often a very dark gray. It is a difficult product to apply evenly, offers minimal protection and is generally best used for small repair jobs and touch-ups. “Hot” bluing is an alkali salt solution, referred to as “Traditional Caustic Black” that is elevated to a temperature between 270° to 310°F [135-154°C]. This method is an expensive process and was adopted by larger firearm companies for large scale bluing by volume in order to achieve economical bluing. It does provide good rust resistance, but the chemicals are highly caustic. “Rust Bluing” is best for rust and corrosion resistance because the process converts any metal that is capable of rusting into magnetite. Treating with an oiled coating enhances the protection offered by the bluing. This process is the only process to safely re-blue vintage shotguns. Many double barreled shotguns are silver brazed together and many of the parts are attached by that method. The higher temperatures of other processes as well as their caustic ingredients can weaken the brazed joints and make the shotgun hazardous to use – only if the brazing has been weakened.
BOLT ACTION: A type of firearm action in which the weapon's bolt is operated manually by the opening and closing of the breach [barrel] with a small handle. As the handle is operated, the bolt is unlocked, the breech is opened, the spent shell casing is ejected, the firing pin is cocked, and a new round/shell [if available] is placed into the breech and the bolt closed.
BOLT THRUST or BREECH PRESSURE: The amount of rearward force exerted by the propellant gases on the bolt or breech of a firearm action or breech when a projectile is fired. The applied force has both magnitude and direction, making it a vector quantity. 
BORE: Interior portion of the barrel that does not include the chamber. It may be smoothed or rifled.  
BORE DIAMETER: The diameter of a gun barrel's interior. In rifled barrels the measurement is from the highest point of the spiraled grooves.  
BORESIGHT: Crude adjustments made to an optical firearm sight, or iron sights, to align the firearm barrel and sights for shooting accuracy. This method is usually used to pre-align sights, which makes zeroing [zero drop at XX distance] much faster. Used by manufacturers who install and include optical sights with firearms purchased out of the box. 

BORE SNAKE: A tool used to clean a barrel of a gun, basically a rope with a pull handle on one end and a device for attaching a cleaning tip, commonly used for field cleaning in a field cleaning kit.
BRASS: Empty cartridge case, commonly made of brass, but some national military rounds are steel but are still referred to as brass.
BREAK-ACTION: A firearm whose barrels are hinged, and rotate perpendicular to the bore axis to expose the breech and allow loading and unloading of ammunition. 
BUCKSHOT: Type of shotgun shot loaded into shotshell cases and consist of large lead pellets that range from .20 to .36 inches in diameter. The load is intended for hunting deer and large-game. 
BULLET, ARMOR PIERCING: A firearm projectile designed to penetrate armor. Manufacture and sale of armor piercing bullets for non-military and law enforcement use is prohibited by the Gun Control Act of 1968.  
BULLET, HOLLOW POINT: A type of bullet designed to expand upon impact, which lessens the depth of penetration. Typically used by law enforcement for self-defense and by hunters to avoid over-penetration and thereby reducing the chance of innocent people being hurt by bullets passing through the body of target.  
BULLET, WADCUTTER:  Bullet designed for target shooting with a cylinder shape and pointed nose, it cleanly perforates target paper, leaving behind a clear, identifiable entry point ideal for precise scoring. 
BULLPUP: a firearm configuration where both the action and magazine are located behind the trigger.
BURST MODE: a firing mode enabling the shooter to fire a predetermined number of rounds with a single pull of the trigger. The M16-A2 fires a burst of three rounds in burst mode when selector is turned to BURST. 
BUTT: The rear end of a firearm, opposite to the muzzle. It is the bottom portion of the handle on handguns and the end of the stock on shotguns and rifles.  
BUTTON RIFLING: Rifling that is formed by pulling a die made with reverse image of the rifling [the “button”] down the pre-drilled bore of a firearm barrel. See also cut rifling and hammer forging.

CALIBER or CALIBRE: (1) in small arms, the internal diameter of a firearm's barrel or a cartridge’s bullet, usually expressed in millimeters or hundredths of an inch; in measuring rifled barrels this may be measured across the lands [as .303 British] or grooves [as .308 Winchester]. (2) A specific cartridge for which a firearm is chambered, as .44 Magnum. (3) in artillery, the length of the barrel expressed in terms of the internal diameter, for example, a 3-inch, 30 caliber gun would have a barrel 3 inches in internal diameter and 90 [30 times 3] inches in length.
CARBINE: (1) a shortened version of a service rifle, often chambered in a less potent cartridge. The M4 Carbine is an example which uses the same cartridge but a shorter barrel, whereas the M1 Carbine is an example using a different cartridge. (2) a shortened version of the infantryman's musket or rifle suited for use by cavalry troops.
CARTRIDGE: the assembly consisting of a bullet, gunpowder, shell casing, and primer. When counting, it is referred to as a round.
CARTRIDGE, MAGNUM: A specially designed cartridge that produces greater bullet velocity, or a shotshell containing more shot than standard for a firearm. 
CARTRIDGE, RIMFIRE: A complete, single round of ammunition with the primer located within the metal rim of the casing. Commonly .22 rifles use rimfire cartridges. 
CASELESS AMMUNITION: a type of small arms ammunition that eliminates the cartridge case that holds the primer, propellant, and projectile together as a unit.
CASKET MAGAZINE: a quad [four] stack box magazine.
CENTERFIRE: a cartridge in which the primer is located in the center of the cartridge case head. Unlike rimfire cartridges, the primer is a separate and replaceable component. The centerfire cartridge has replaced the rimfire in all but the smallest cartridge sizes. Except for low-powered .22 and .17 HMR caliber cartridges, and certain antique firearms, all modern pistols, rifles, and shotguns used centerfire ammunition. 
CHAIN GUN: a type of machine gun or autocannon that uses an external source of power to cycle the weapon.
CHAMBER: the portion of the barrel or firing cylinder where the cartridge is inserted prior to being fired. It prevents expansion of the case as the propellant ignites. Rifles and pistols generally have a single chamber in their barrels, while revolvers have multiple chambers in their cylinders and no chamber in their barrel.
CHAMBERING: Inserting a round into the chamber, either manually or through the action of the weapon [IE, pump-action, lever-action, bolt-action, or automatic-action].
CHARGER: a speedloader that holds several cartridges together in a single unit for easier loading of a firearm's magazine. A stripper clip is used only for loading the magazine and is not necessary for the firearm to function.
CHOKE: a tapered constriction of a shotgun barrel's bore at the muzzle end. Chokes are almost always used with modern hunting and target shotguns to improve performance.
CLIP: a device that is used to store multiple rounds of ammunition together as a unit, ready for insertion into the magazine of a repeating firearm. This speeds up the process of loading and reloading the firearm as several rounds can be loaded at once. The term clip is erroneously used to describe a firearm magazine because the clip feeds ammunition to a magazine or revolving cylinder, while a magazine or belt is used to load cartridges into the chamber of a firearm ready for firing.
COLLATERAL DAMAGE: Damage that is unintended or incidental to the intended outcome. The term originated and is used by US military personnel, but has expanded into civilian terminology.
COLLIMATOR SIGHT: a type of optical “blind” sight that allows the user looking into it to see an illuminated aiming point aligned with the device the sight is attached to no matter what position of the eye [parallax free]. The user can not see through the sight so it is used with both eyes open while one looks into the sight, with one eye open and moving the head to alternately see the sight and then at the target, or using one eye to partially see the sight and target at the same time. Another description often used is occluded eye gunsight [OEG].
COMBINATION GUN: a shoulder-held firearm that has two barrels; one rifle barrel and one shotgun barrel. Most combination guns are over/under designs [abbreviated as O/U] where two barrels are stacked vertically on top of each other, but some combination guns are side-by-side in design [abbreviated as SxS] – where two barrels are beside each other, brazed together.
CORDITE: Smokeless propellant that was developed and produced in the United Kingdom from 1889 to replace gunpowder as a military propellant. Cordite is classified as a low explosive, like gunpowder, because it burns slowly and has low brisance. The hot gases produced by burning gunpowder or cordite generate enough pressure to propel a bullet or shell to its target, but not enough to destroy the barrel of the firearm.
CQC: Close Quarters Combat or Close Quarters Battle [CQB] is a type of fighting where small units engage the enemy with personal weapons at short range, sometimes to the point of hand-to-hand combat or fighting with hand weapons such as bayonets or knives.
CYLINDRO-CONOIDAL BULLET: a hollow base bullet that is shaped in a way that when fired, the bullet expands and seals the bore. It was invented by Captain John Norton of the British 34th Regiment in 1832, after he examined blow pipe arrows used by natives in India and found their base was formed of elastic locus pith, which by its expansion against the inner surface of the blow pipe prevented the escape of air past it.

DAMASCUS BARREL or DAMASCUS TWIST: an obsolete method of manufacturing a firearm barrel made by twisting strips of metal around a mandrel and forge welding it into shape. 
DECOCKER: Most traditional double-action semiautomatic pistols are designed to be carried with the hammer down [uncocked] on a chambered round, with or without a manual safety engaged. A decocker or manual decocking lever allows the hammer to be dropped on a live cartridge without risk of discharging it, usually by blocking the hammer or retracting or covering the firing pin before releasing the sear. It eliminates the need to pull the trigger or to control the fall of the hammer. Some systems are three-way, like Heckler & Koch pistols. The Walther PP and Beretta 92 use a two-way system, where engaging the safety also decocks the firearm.
DERRINGER: A type of  firearm usually designed with two barrels, side-by-side or over-under, with a single frame. 
DIRECT IMPINGEMENT: a type of gas operation for a firearm that directs gas from a fired cartridge directly to the bolt carrier or slide assembly to cycle the action.
DOGLOCK: The lock that preceded the “true” flintlock rifles and pistols in the 17th century. It was commonly used in Europe in the 1600s. It was popular with British and Dutch military. A doglock carbine was the principle weapon of the harquebusier, the type most often used by the cavalry of armies of the Thirty Years War and the English Civil War eras.
DOUBLE-ACTION: In semiautomatics, the double-action trigger mechanism is identical to the double-action revolver; however, the firing mechanism automatically cocks the hammer or striker after the gun is fired. This mechanism will cock and release the hammer when the hammer is in the down position, but on the next shot, the trigger will function as a single action. The Beretta Model 92 is a good example of a Double-Action/Single-Action combination semiautomatic pistol. On many pistols, including the Beretta, there is the option to cock the hammer before firing the first shot. This removes the heavy pull of the double-action. Often there is a decocker to return the pistol to double-action. Double-action revolvers can be fired in either mode by pulling the trigger or manually by cocking the hammer [single-action]. For example, the Colt Python does not have to be fired in double-action mode.
DOUBLE-BARRELED SHOTGUN: a shotgun with two barrels, usually of the same gauge or bore. The two types of double-barreled shotguns are over/under [O/U] where two barrels are stacked on top of each other, and side-by-side [SxS] where two barrels sit beside each other. Double-barreled firearms that use one shotgun barrel and one rifle barrel is called combination gun.
DOUBLE RIFLE: a rifle that has two barrels, usually of the same caliber. The two types of double rifles are over/under [O/U] where two barrels are stacked on top of each other, and side-by-side [SxS], similarly to a double-barreled shotgun.
DRILLING: a firearm with three barrels [German word drie for three] … typically it has two barrels side-by-side on the top, with a third barrel underneath. It is primarily used for taking winged animals as well as big game. It is also used in jurisdictions where a person is only allowed to own a single firearm.
DRUM MAGAZINE: a type of firearm magazine that is shaped like a cylinder [drum].
DRY FIRE: the practice of “firing” a firearm without ammunition by pulling the trigger and allowing the hammer or striker to drop on an empty chamber.
DUM-DUM: a round of ammunition that is inert – no primer, no propellant, no explosive charge. It is used for weapon function checks and for crew training. Unlike a blank, it has no charge at all. [Also called a dummy round].

EJECTOR: In a semi-automatic rifle, pistol, or shotgun; it is a stationary pin that pushes cartridge cases out of and away from the firearm during the recoil process. In a revolver, the device often is a star shaped component connected to the ejector rod to assist in speedy cartridge removal. 
EJECTOR ROD: The rod used to unload the cartridges and/or cases from a firearm.
ELECTRONIC FIRING: Using electric current to fire a cartridge instead of a percussion cap. The electric current ignites the propellant and fires the cartridge as soon as the trigger is pulled. CVA is one manufacturer that produced electric firing muzzle loaders to reduce the time loading and not requiring a primer cap to ignite the powder to propel the ball/conical bullet down range. Electric trigger mechanisms are also used in heavy caliber armed forces weapons, like the 20-millimeter “VulcanM61 Cannon gatling gun or other large caliber gatling guns.
EYE RELIEF: For optics such as binoculars or a rifle scope, eye relief is the distance from the eyepiece to the viewers eye which matches the eyepiece exit pupil to the eye's entrance pupil. Short eye relief requires the observer to press his or her eye close to the eyepiece in order to see an unvignetted image. For a shooter, eye relief is important and a safety concern. An optic with too short of an eye relief can cause a skin cut at the contact point between the optic and the eyebrow of the shooter due to recoil action.
EXPANDING BULLET: a bullet designed to expand on impact, increasing in diameter to limit penetration and/or produce a larger diameter wound. The two typical designs are the hollow point bullet and the soft point bullet. The Hague Convention of 1899, Declaration III, prohibits the use of expanding bullets in international warfare. The Geneva Convention, contrary to belief, does not mention this restriction. Because the Hague convention restriction only applies to war, expanding rounds remain legal for civilian use, for example hunters use it to prevent loss of a game animal and to ensure a humane death of vermin. Law enforcement or civilians in self defense, use expanding bullets to prevent collateral damage caused by bullets passing through the aggressor and injuring innocent people. [See Also: Frangible and Stopping Power]
EXTRACTOR: a part of a firearm that serves to remove brass cases of fired ammunition after the ammunition has been fired. When the gun's action cycles, the extractor lifts or removes the spent brass casing from the firing chamber.

FALLING BLOCK ACTION: [also Sliding-Block Action] a single-shot firearm action in which a solid metal breechlock slides vertically in grooves cut into the breach of the rifle and actuated by a lever. When in the top position, it is locked and resists the force of recoil while sealing the chamber. In the lower position, it leaves the chamber open to be loaded by a cartridge from the rear.
FERRITIC NITROCARBURIZING: A case hardening process that diffuse nitrogen and carbon into ferrous metals at sub-critical temperatures to improve scuffing resistance, fatigue properties and corrosion resistance of metal surfaces. It is also called nitriding.
FIRE FORMING: The process of reshaping a metallic cartridge case to fit a new chamber by firing it within that chamber. 
FIRING PIN: A component forced into the primer of a cartridge by the force of the hammer that results in a controlled explosion that launches the projectile [bullet]. A spring driven firing pin on guns with no hammer is used, such as for a Glock, and is called a Striker.  
FLASH SUPPRESSOR: An accessory that attaches to the muzzle of a firearm and disperses the ignited gases in order to restrain muzzle flash.  
FORCING CONE: The tapered section at the rear of the barrel of a revolver that eases the entry of the bullet into the bore.
FULL COCK: Refers to the hammer fully retracted into firing position; a pistol ready for firing. 
FOULING SHOT: a shot fired through a clean bore, intended to leave some residue of firing and prepare the bore for more consistent performance in subsequent shots. The first shot through a clean bore will behave differently then subsequent shots through a bore with traces of powder residue, resulting in different point of impact. [See Fouling Shot Journal, a publication of the Cast Bullet Association].
FORWARD ASSIST: a button found on the M16 and AR-15 rifles, located near the bolt closure where when hit will push the bolt carrier forward to ensure the bolt is locked. Found in the earlier models, the more modern models do not require to have a forward assist, as in Model M16-A1 and M16-A2 and AR-15s.
FOULING: The accumulation of unwanted material on solid surfaces. Fouling material can consist of powder, lubrication residue, or bullet material such as lead or copper.
FRANGIBLE: a bullet that is designed to disintegrate into tiny particles upon impact to minimize their penetration for reasons of range safety, to limit environmental impact, or to limit the danger behind the potential target. Two examples are: Glaser Safety Slug and a breaching round.
FRIZZEN: an “L” shaped piece of steel hinged at the rear used in flintlock firearms. The flint scraping the steel causes a shower of sparks to be thrown into the flash pan.

GAS CHECK: a device used in some types of firearms ammunition when non-jacketed bullets are used in high pressure cartridges.
GAS-OPERATED RELOADING: a system of operation used provide energy to operate autoloading firearms.
GAUGE: The gauge of a firearm is a unit of measurement used to express the diameter of the barrel based upon the weight of the largest lead ball the firearm can discharge. The only exception is the .410 shotgun that refers to the actual diameter of the barrel.
GENERAL PURPOSE MACHINE GUN: a machine fun intended to fill the role of either a light machine gun or medium machine gun, while at the same time being more portable.
GRAIN: a unit of measurement used in firearms to denote the amount of powder in a cartridge or the weight of a bullet, as used in weighing grain of wheat or barley, but since 1958, the grain [gr] measure has been redefined using the International System of Units as precisely 64.798 mg. There are 7,000 grains per avoirdupois pound in the Imperial and US customary units.
GRIP SAFETY: a safety mechanism, usually a lever on the rear of a pistol grip, that automatically unlocks the trigger mechanism of a firearm as pressure is applied by the shooter's hand. 
GROUPING/GROUP: The pattern of bullets fired at a target in succession without changing the aiming point; often used to determine performance accuracy in rapid fire circumstances and to adjust sighting.  
GUNPOWDER: also called black powder, it is a mixture of sulfur, charcoal, and potassium nitrate. It burns rapidly and produces a volume of hot gas made up of carbon dioxide, water [H2O] and nitrogen, and a solid residue of potassium sulfide. Because of its burning properties
and the amount of heat and gas volume that it generates, gunpowder is widely used as a propellant in firearms and as a pyrotechnic composition in fireworks. Modern firearms do not use traditional black powder, but instead uses smokeless powder.

HAIR TRIGGER: A trigger that requires a small amount of force to depress. Often used for target practice or competition shooting, it provides a more consistent aim and steady repeated shooting. Not recommended for combat or self-defense or concealed-carry handguns. 
HALF COCK: A safety notch  built into the hammer where it clicks into place at the halfway point. In single-action Old West handguns, it was intended to prevent accidental dropping of the hammer. 
HAMMER BITE: The action of an external hammer pinching or poking the web of the operator's shooting hand between the thumb and fore-finger when the gun is fired. Some handguns are prone to this like the M1911 and Browning Hi-Power pistols. 
HAMMERLESS:  A specific firearm design where the hammer or striker is integrated into the firearm's interior. 

JACKETED BULLETS: [also – full-metal jacket bullet] a bullet that has a soft core (usually lead) encased in a shell of harder metal, like cupronickel , gliding metal or a steel alloy. A full-metal jacket extends completely around the bullet. The jacket allows for higher muzzle velocities than bare lead without depositing amounts of metal in the bore. It also prevents damage to bores from steel or armor-piercing core materials. The FMJ [full-metal jacket] is easily recognized from hollow-point or soft-point bullets. The first successful full-metal jacket rifle bullets were invented by Lt. Col. Eduard Rubin of the Swiss Army in 1882. Full-metal jackets were first used as standard ammunition in 1886 for the French Mle 1886 Lebel Rifle. Full-metal jacket bullets produce smaller entry wound sizes than soft-tipped bullets and can be used against soft or hard targets. 
JAM: A generic term used when referring to any firearm malfunction that involves failure of moving parts, faulty ammunition, poor maintenance, or misuse.  
JEWELING: a cosmetic process to enhance the looks of firearm parts, such as the bolt. The look is created with an abrasive brush and compound that roughs the surface of the metal in a circular pattern.

KEYHOLE or KEYHOLING: Refers to the shape of the hole left in paper target by a bullet fired down a gun barrel which has a diameter larger than the bullet or which fails to properly stabilize the bullet. A bullet fired in this manner tends to wobble or tumble as it moves through the air and leaves a “keyhole” shaped hole in a paper target instead of a round one.
KYBER PASS COPY: a firearm manufactured by cottage gunsmiths in the Kyber Pass region between Pakistan and Afghanistan.

LANDS: In rifled barrels these are the treads or raised portions in relation to the grooves. 
LENGTH OF PULL: The distance between the trigger and the butt end of the stock of a rifle or shotgun.
LEVER-ACTION: a type of firearm action which uses a lever located around the trigger guard area, often including the trigger guard itself, to load fresh cartridges into the chamber of the barrel when the lever is worked.
LIGHT MACHINE GUN: a machine gun designed to be employed by an individual soldier.
LIVE FIRE EXERCISE [LFX]: Any exercise in which a realistic scenario for the use of specific equipment is simulated. In the popular terminology this is applied primarily to tests of weapons or weapon systems that are associated with the various branches of a nation's armed forces, although the term can be applied to the civilian arena as well.
LOCKED-BREACH: [Also see Recoil] A system designed for more powerful pistols like 9mm Parabellum and .45 ACP needed to retard breech opening requiring a heavy slide and stiff spring, which makes them bulkier than blowback design models. In the classic locked-breech pistol, the barrel is locked to the slide, but the slide is not locked to the frame [receiver]. Some have tilting barrels with locking lugs on top of the barrel [1911, High Power, and Neuhausen]; while others have a separate locking block to connect barrel and slide like P-38, Lahti, and Beretta. Luger is unique from the other two types in that is uses a toggle action that is less commonly seen; however, all are locked-breech actions.
LOAD: A general term that refers to all the component parts of a cartridge. It is also the act of placing ammunition in the chamber of a firearm or the amount of powder in a cartridge or hand-loaded blackpowder muzzle loading firearm.
LUG: Any piece that projects from a firearm for the purpose of attaching something to it. For example, barrel lugs are used to attack a break-action shotgun barrel to the action itself. If the firearm is a revolver, the term may also refer to a protrusion under the barrel that adds weight, thereby stabilizing the gun during aiming, mitigating recoil, and reducing muzzle flip. A full lug extends all the way to the muzzle, while a half lug extends partially down the barrel. ON a swing-out cylinder revolver, the lug is slotted to accommodate the ejector rod.


MACHINE GUN: a fully automatic mounted or portable firearm.
MACHINE PISTOL: A handgun-style fully automatic or burst-mode firearm.
MACHINE REVOLVER: A revolver that uses the energy of firing for cocking the hammer and revolving the cylinder, rather than using manual operations to perform these actions. A more correct term is semi-automatic revolver.
MAGAZINE: A magazine is an ammunition storage and feeding device within or attached to a repeating firearm. Magazines may be integral to the firearm [fixed] or removable [detachable]. The magazine functions by moving the cartridges stored in the magazine into a position where they may be loaded into the chamber by the action of the firearm. Magazines are often mistakenly called “clips” [by civilians] - which is an entirely different mechanism. 
MAINSPRING: The spring which drives the firing pin of a firearm. It is part of the action assembly.  
MATCH GRADE: Firearm parts and ammunition that are suitable for a competitive match. This refers to parts that are designed and manufactured in such a way that they have tight tolerances and a high level of accuracy.

MOA: {Minute of Angle) ... an angular measurement 1/60th of a degree. 1 MOA spreads about 1" per 100 yards. 1 MOA is  different size at different distances - 8" spread at 800 yards. The following NSSF video explains MOA, important for long-range, scoped rifles used by military snipers, hunters, and competition long-range shooting.
Important factors concerning MOA: (1) always think in increments of 1 MOA at any distance, (2) determine how many 1 MOA adjustments are required in adjustment, and (3) when changing scope adjustment, think in MOA, not 'clicks'. 
MUZZLE: The part of a firearm at the end of the barrel from which the projectile will exit.
MUZZLE BRAKES and RECOIL COMPENSATORS: Devices that are fitted to the muzzle of a firearm to redirect propellant gases with the effect of countering both recoil and unwanted rising of the barrel during rapid fire.
MUZZLE ENERGY: The kinetic energy of a bullet as it is expelled from the muzzle of a firearm. It is often used as a rough indication of the destructive potential of a given firearm or load. The heavier the bullet and the faster it moves, the higher its muzzle energy and the more damage it will do. 
MUZZLE FLASH: The brief, intense flaring of ignited, expanding gases that emerge from the end of the barrel with the bullet, reacting with the oxygen in the air when a firearm discharges. 
MUZZLE LOADER: Any traditional firearm, pistol, rifle, or shotgun, that is loaded by inserting a powder charge followed by a bullet, lead ball, or shot projectiles through the muzzle. This type of firearm is also called blackpowder firearms.  
MUZZLE VELOCITY: The speed at which a projectile leaves the muzzle of a firearm. Muzzle velocities range from approximately 800 ft/s (240 m/s) for some pistols and older cartridges to more than 4,000 ft/s (1,200 m/s) in modern cartridges such as the .220 Swift and .204 Ruger.

NECKING DOWN or NECKING UP: refers to shrinking or expanding the neck of an existing cartridge to make it use a bullet of a different caliber. A typical process used in the creation of wildcat cartridges
NOSE: The forward tip, usually a narrow point, of a bullet or other projectile. 
NRA [National Rifle Association of America]: an American organization which lists as its goals to protect the Second Amendment of the United States Bill of Rights and the promotion of firearm ownership rights as well as marksmanship, firearm safety, and the protection of hunting and self-defense in the United States. The NRA is also the sanctioning body for most marksmanship competition in the United States from the local level to the Olympic level.

OBTURATE: The process of a bullet expanding under pressure to fit the bore of the firearm, or a cartridge case expanding under pressure to seal the chamber. See also swage.
OUT-OF-BATTERY: The status of a weapon before the action has returned to the normal firing position. The term originates from artillery, referring to a gun that fires before it has been pulled back into its firing position in a gun battery. In firearms where there is an automatic loading mechanism, a condition in which a live round is at least partially in the firing chamber and capable of being fired, but is not properly secured by the usual mechanism of that particular weapon can occur.
OVER-BORE: Small caliber bullets being used in very large cases. It is the relationship between the volume of powder that can fit in a case and the diameter of the inside of the barrel or bore. 
OVER AND UNDER: A double-barrel firearm with two barrels arranged in a vertical configuration, typically a shotgun.  

PARKERIZING: A method of protecting a steel surface from corrosion and increasing its resistance to wear through the application of an electrochemical phosphate conversion coating. Also called phosphating and phosphatizing
PARTRIDGE SIGHT: A type of handgun sight with a semi-rectangular shape.
PATTERN: The arrangement or spread of shot when fired from a shotgun. General measurements are derived from the percentage of pellets that terminate in a 30-inch target area 40 yards from the point of discharge.  
PERCUSSION CAP: a small cylinder of copper or brass that was the invention that enabled muzzle-loading firearms to fire reliably in any weather. The cap has one closed end. Inside the closed end is a small amount of a shock-sensitive explosive material such as fulminate of mercury. The percussion cap is placed over a hollow metal “nipple” at the rear end of the gun barrel. Pulling the trigger releases a hammer which strikes the percussion cap and ignites the explosive primer. The flame travels through the hollow nipple to ignite the main powder charge.
PICATINNY RAIL: A bracket used on some firearms in order to provide a standardized mounting platform.
PINFIRE: an obsolete type of brass cartridge in which the priming compound is ignited by striking a small pin which protrudes radially from just above the base of the cartridge.
PLINKING: informal target shooting done at non-traditional targets such as tin cans, glass bottles, and balloons filled with water.
POWERHEAD: a specialized firearm used underwater that is fired when in direct contact with the target. [also called bang stick
PRIMER: Small compartment of a cartridge containing a combustible material, which when struck with the firing pin or striker, creates the spark that ignites the gunpowder that propels the projectile from the barrel.  
PUMP-ACTION: a rifle or shotgun in which the handgrip can be pumped back and forth in order to eject a spent round of ammunition and to chamber a fresh one. It is much faster than a bolt-action and somewhat faster than a lever-action, as it does not require the trigger hand to be removed from the trigger while reloading. When used in rifles, this action is commonly called a slide action.

QUAD-BARRELLED: a gun, usually artillery, with four barrels, such as the ZPU.

RAMROD: a device used with early firearms to push the projectile up against the propellant [gunpowder].
RATE OF FIRE: the frequency at which a firearm can fire its projectiles.
RECEIVER: The frame or action body portion of a firearm in which the firing mechanism is contained. This part joins the barrel and the stock. It is also called the frame in break-open firearms. 
RECOIL: The backward momentum of a firearm when it is discharged. In technical terms, the recoil caused by the firearm exactly balances the forward momentum of the projectile, according to Newton's third law. [often called kickback or kick]
RED DOT SIGHT: a type of reflector [reflex] sight for firearms that provides a red light-emitting diode as a reticle to create an aim point for low-light conditions.
REFLECTOR (REFLEX) SIGHT: a non-magnifying optical device that has an optically collimated reticle, allowing the user to look through a partially reflecting glass element and see a parallax free cross hair or other projected aiming point superimposed on the field of view. It was invented in 1900 but was not popularly used on firearms until more reliable versions were invented in the late 1970s. It is usually referred to as a reflex sight.
REVOLVER: a repeating firearm that has a cylinder containing multiple chambers and at least one barrel for firing.
RIFLE BEDDING: a process of filing gaps between the action and the stock of a rifle with an epoxy based material.
RIFLING: Helical grooves in the barrel of a gun or firearm, which puts a spin to a bullet around its long axis. This spin serves to gyroscopically stabilize the bullet and improve its aerodynamic stability and accuracy. Also refers to the process of machining the grooves of a barrel. 
RIMFIRE: a type of firearm cartridge that uses a firing pin which strike's the base's rim instead of striking the primer cap at the center of the base of the cartridge to ignite [centerfire cartridge]. The rim of the rimfire cartridge is an extended and widened percussion cap which contains the priming compound, while the cartridge case itself contains the propellant powder and projectile [bullet].
ROLLING BLOCK: a form of firearm action where the sealing of the breech is done with a circular shaped breechlock able to rotate on a pin. The breechlock is locked into place by the hammer, thus preventing the cartridge from moving backwards at the moment of firing. By cocking the hammer, the breechlock can be rotated freely to reload the weapon.

SABOT: a device used in a firearm to fire a projectile, such as a bullet, that is smaller than the bore diameter.
SAFETY: a mechanism used to help prevent the accidental discharge of a firearm, helping to ensure safer handling. Safeties can be divided into subtypes such as internal safeties and external safeties. Sometimes they are called “passive” and “active” safeties or “automatic” and “manual”.
SAWED-OFF SHOTGUN [SBS]: a type of shotgun with a shorter barrel often a shorter or deleted stock.
SEAR: The part of a firearm [automatic and semi-automatic] that prevents more than one shot from being fired at one time. 
SELECTIVE FIRE: a firearm that fires semi-automatically and at least one automatic mode by means of a selector depending on the weapon's design. Some selective fire weapons use burst fire mechanisms to limit the maximum or total number of sots fired automatically in this mode. The most common limits are two or three rounds per pull of the trigger. The M16A2 has a three-round burst mode.
SEMI-WADCUTTER [SWC]: a type of all-purpose bullet commonly used in revolvers which combines features of the wadcutter target bullet and traditional round-nosed revolver bullets, and is used for hunting, target shooting, and plinking. The design consists of a conical nose, truncated with a flat point, sitting on a cylinder. The flat nose punches a clean hole in the target and the sharp shoulder enlarges the hole neatly, allowing easy and accurate scoring of the target. 
SHOTSHELL:  A complete round of shotgun ammunition consisting of multiple pellets [shot], propellant, primer, and casing. Also known as a shotgun shell
SIGHT RADIUS: The distance between the front and rear sights. The longer the radius the more accurate the sights will be. 
SINGLE-ACTION (SA): usually refers to a pistol or revolver, single-action is when the hammer is pulled back manually by the shooter (cocking it), after which the trigger is operated to fire the shot. [see also double-action]
SLAMFIRE: a premature, unintended discharge of a firearm that occurs as a round is being loaded into the chamber.
SLEEVING: a method of using new tubes to replace a worn-out barrel.
SLIDE: The part of the action on a semi-automatic or automatic that moves back and forth to eject an empty case and reload a loaded cartridge from the magazine. 
SLIDE BITE: a phenomenon that is often related to hammer bite. In this case the web of the shooting hand is cut or abraded by the rearward motion of the semi-automatic pistol's slide, not by the gun's hammer. It most often occurs with small pistols like the Walther PPK and Walther TPH that have an abbreviated grip tang. This problem is caused most often by sharp machining found on firearms.
SMOKELESS POWDER: the name given to propellants used in firearms and artillery that produce a small amount of smoke when fired, unlike black powder. The term is generally not used in other English speaking countries beyond the United States, adopting the term Cordite. Smokeless powder allowed the development of modern semi-auto and fully automatic firearms and lighter breeches and barrels for artillery. It burns cleaner than black powder and thus is not apt to foul moving parts. Smokeless powders are classified as division 1.3 explosives and is regulated by the US ATF. Various types of smokeless powder, including pellets, has a nitro-based chemical that makes it burn cleaner. Muzzle-loading rifles made after 1984 are designed to use smokeless powder loads as well as sabot bullets instead of traditional lead balls. Muzzle loaders are delighted because they need not worry as much about corrosion as the traditional black powder causes. After every twenty five shots, the breech plug is removed with a 5/8-inch socket wrench and the barrel is cleaned out with a twenty gauge shotgun brass or stainless steel brush and cleaned like any modern high-power rifle. When cleaning with black powder, the barrel must be cleaned with a 20 gauge brass or stainless steel shotgun brush followed by a soap and water bath. However, all powder loads must be measured carefully to prevent too much stress on the barrel. Except for custom barrels on other manufactured muzzle loaders, Savage is the major source for out-of-the-box muzzle loaders safe enough to use smokeless powder. Reenactment units often prefer to use the old traditional black powder in their firearms because of its “authentic” signature of smoke when fired. CVA for example stresses that only black powder be used in their firearms. Make sure your barrel can stand the stress of the smokeless powder before using it.
SPEEDLOADER: a device used for loading a firearm or firearm magazine with loose ammunition quickly. Speedloaders are generally used for loading all chambers of a revolver at once, although speedloaders of different designs are also used for loading a fixed tubular magazine for a shotgun or rifle, or the loading of box or drum magazines. Revolver speedloaders are used for revolvers having either swing-out cylinders or top-break cylinders.
SPORTERIZING: The practice of modifying military-type firearms either to make them suitable for civilian sporting use or to make them legal under the law. 
SPUR: The projection on the hammer used to pull the hammer when cocking.  Sometimes refers to the machined area of a trigger, sear and other action parts.  
SQUIB LOAD: a firearms malfunction in which a fired projectile does not have enough force behind it to exist the barrel, and thus becomes stuck.
STOCK: The part of a rifle or other firearm where the barrel and firing mechanism are attached and held against one's shoulder when firing the gun. The stock provides a means for the shooter to firmly support the device and easily aim it.
STOPPING POWER: The ability of a firearm or other weapon to cause a penetrating ballistic injury to a target, human, or animal sufficient to incapacitate the target where it stands.
STRIPPER CLIP: A speedloader that holds several cartridges together in a single unit for easier loading of a firearm's magazine. A stripper clip is used only for loading the magazine and not necessary for the firearm to function. Magazines are sometimes mistakenly referred to as “clips”.
SUPPRESSOR [also sound suppressor, sound moderator, silencer]: a device attached to or part of the barrel of a firearm to reduce the amount of noise and flash generated by firing the weapon. Suppressors are restricted by the US federal government and can only be obtained, used or manufactured with a special licensing/registration and the suppressor must have a identification serial number stamped on its surface. 
SWAGE: To reduce an item in size by forcing through a die. In internal ballistics, swaging refers to the process where bullets are swaged into the rifling of the barrel by the force of the expanding powder gases.
SWAGED CHOKE: a constriction or choke in a shotgun barrel formed by a swaging process that compresses the outside of the barrel.
SWAGED RIFLING: Rifling in a firearm barrel formed by a swaging process, such as button rifling.

TAYLOR KO FACTOR: a mathematical approach for evaluating the stopping power of hunting cartridges.
TELESCOPING STOCK or COLLAPSING STOCK: a stock on a firearm that telescopes or folds in on itself in order to become more compact. Telescoping stocks are useful for storing a rifle or weapon in a space that it would not normally fit.
TERMINAL BALLISTICS: a sub-field of ballistics – the study of the behavior of a projectile when it hits its target. 
TRIGGER LOCK: A safety accessory that inhibits depression of the trigger. These are recommended for use with unloaded firearms because removing the lock may apply enough force to the trigger where accidental discharge will occur. 
TRIGGER PULL: The amount of force required to fully depress the trigger of a firearm that is expressed in pounds. This force can vary, depending upon firearm type, with target firearms requiring only about one pound pressure and double-action firearms requiring about 15 pounds.  
TRUNNION: a cylindrical protrusion used as a mounting and/or pivoting point. On firearms, the barrel is sometimes mounted on a trunnion, which in turn is mounted to the receiver.

UPSET FORGING: a process that increases the diameter of a workpiece by compressing its length.
UNDERLUG: (1) locking lugs on a break-action firearm that extend from the bottom of the barrels under the chamber(s) and connect into the receiver bottom. (2) the metal shroud underneath the barrel of a revolver that surrounds and protects the extractor rod. The two types of underlugs include half-lug and full-lug [full-length of barrel].

VARMINT RIFLE: a small-caliber rifle or high-powered air gun primarily used for varmint hunting – killing non-native or non-game animals such as rats, house sparrows, starling, crows, ground squirrels, gophers, jackrabbits, marmots, groundhogs, porcupine, opossum, coyote, skunks, weasels, or feral cats, dogs, goats, pigs and other animals considered to be nuisance vermin destructive to native or domestic plants and animals. 
VELOCITY: The rapidity or speed of a projectile. The standard unit is feet per second. [F/S] 

WADCUTTER: a special-purpose bullet designed for shooting paper targets, usually at close range and at subsonic velocities, usually under 800 ft/s (240 m/s). Often used in handguns and airgun competitions. A wadcutter has a flat or nearly flat front that cuts a clean hole in paper targets making it easier to score and in favor of the shooter.
WHEELLOCK: an obsolete mechanism for firing a firearm.
WILDCAT CARTRIDGE: a custom cartridge which ammunition and firearms are not mass-produced. The cartridges are often created in order to optimize certain performance characteristics (power, size, or efficiency) of an existing commercial cartridge. [see improved cartridge]
WINDAGE: The side-to-side adjustment of a sight, used to change the horizontal component of the aiming point. (see Kentucky windage)

X-RING: a circle in the middle of a shooting target bullseye used to determine winners in event of a tie.

YAW: The heading of a bullet, used in external ballistics that refers to how the Magnus effect causes the bullet to move out of a straight line based on their spin.

ZERO-IN or ZEROING: The act of setting up a telescopic or other sighting system so that the point of impact of a bullet matches the sights at a specified distance.