This page contains definitions of all the terms in our gun glossary. To find a particular term, use our quick reference menu of links.

ACP ammunition
Abbreviation for Automatic Colt Pistol and used with caliber designations such as 25 ACP, 32 ACP, 380 ACP, and 45 ACP.
action
The working mechanism of a firearm that loads the cartridge, fires the cartridge, extracts and ejects the spent cartridge case.
air gun
A gun that uses compressed air or gas to propel a projectile.
ammunition
The projectiles fired from guns. The term also includes the fuses, propelling charges, or primers of the projectiles.
automatic
The working mechanism of a firearm that feeds cartridges, fires, extracts and ejects cartridge cases for as long as the trigger is fully depressed and cartridges remain in the feeding system. Compare semi-automatic.
ball
The round lead projectile usually wrapped in a greased fabric patch and fired by muzzleloading firearms.
ball ammunition
A term generally used by the military for a cartridge with a full metal jacketed bullet or solid metal projectiles.
ballistics
The study of what happens to moving projectiles. Internal/Interior Ballistics studies what happens inside the firearm from the moment of ignition until it leaves the barrel. Exterior/External Ballistics studies the motion of the projectile after it leaves the barrel. Terminal Ballistics studies the projectile's impact on the target.
barrel
The tube through which the bullet or shot charge passes when the firearm is fired and gases created by the ignition of the powder or compressed air act as the projectile's propellant. May be rifled or smooth.
barrel liner
An insert of special material placed in a barrel to reduce bore erosion, renew an eroded bore. They are also used to strengthen a barrel or alter the diameter to accept a different caliber of ammunition. Also called a sleeve.
barrel lug
A general term for any projection extending at right angles to the barrel.
barrel whip
The movement of the barrel as the projectile moves through it.
barreled action
A rifle or shotgun lacking only the stock.
base
The portion of the cartridge case that contains the primer, also called the head.
BB ammunition
In Shotgun shells, BB shot has a diameter of .180 inches. For use in airguns, a BB is .175 inches in diameter.
belt
The narrow band around the rear section of a cartridge case and forward of the extractor groove that is intended to strengthen the case and usually associated with magnum calibers.
black powder
A finely ground mixture of three basic ingredients: saltpeter (potassium nitrate), charcoal (carbon), and sulfur.
blind box magazine
An integral magazine with a permanently closed bottom.
blowback action
A system where the pressure and energy from the cartridge discharge pushing rearward against the empty cartridge case is used to operate the unloading and loading cycle of a semi-automatic or automatic firearm.
boattail
A tapered rear end of a bullet designed to increase ballistic efficiency at long range.
bolt action
The two main types of bolt action are the turn bolt and straight pull. The bolt action is manually operated by means of a steel rod or handle-like assembly that contains the means to lock a cartridge into the barrel or chamber (located at the rear of the chamber into which the cartridge or propellant is inserted), the firing pin, and the mechanism to extract and eject the spent cartridge case.
bore
The interior or tunnel down the barrel and forward of the chamber through which the projectiles travel.
box lock action
This type of action is usually found on double-barrel shotguns. The hammer and hammer springs are located within the frame or receiver (the basic unit of a firearm that contains the firing and breech mechanism and to which the barrel and stock are attached). The trigger assembly is in the lower tang (the rearward projecting tongue on a receiver or frame to which the buttstock is attached).
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.
breech
The rear of the barrel into which the cartridge or propellant is inserted. Also called chamber.
breech bolt
The locking and cartridge head support mechanism of firearms that operate in line with the axis of the bore.
breech face
That part of the breechblock or breech bolt against which the head of the cartridge case or shotshell rests during firing.
breechblock
The part of the action that fits securely against the cartridge keeping it snug in the breech and locks the action to allow maximum efficiency and safety during firing.
buck & ball
A cartridge containing a round ball and shot.
buckshot
Large lead pellets ranging in size from .20 inches to .36 inches in diameter used in shotshells.
bullet
A single, non-spherical projectile fired from a rifled barrel.
bullet drop
The normal fall from a bullet during its flight from the firearm to the target resultant from the influence of gravity.
bullet jump
bullet jump - The distance a bullet must travel from its place in the cartridge case to the initial engagement of the barrel's rifling.
bullet mushroom
A bullet that has expanded upon impact to a mushroom-like shape.
bullet ogive
The curved forward part of a bullet.
bullet stabilization
The act of steadying a bullet in flight by use of the proper rifling twist and bullet velocity.
butt
In a handgun, the butt is the bottom part of the grip or grip frame. In a rifle or shotgun, it is the rear or shoulder end of the stock.
butt plate
This is the covering made of metal, rubber, plastic or other materials that protects and reinforces the butt of the firearm stock.
caliber
A numerical term, without the decimal point, in a cartridge's name to indicate the nominal bullet diameter.
carbine
A light, short-barreled rifle.
cartridge
A single unit of ammunition consisting of the case, primer, and propellant with one or more projectiles. Modern cartridges generally fall into one of three categories: centerfire with the primer seated in the center of the base, rimfire where the primer powder is sealed in the soft rim around the base, and shotshells that include shot or small pellets instead of a single bullet.
caseless ammunition
Ammunition that has the propellant charge molded to the base of the bullet and not enclosed in any type of cartridge case.
centerfire cartridge
A cartridge with the primer seated in the center of the base.
chamber
The rear of the barrel into which the cartridge or propellant is inserted. Also called breech.
chamber throat
The area forward of the cartridge chamber extending to the point where the bore begins to have its full bore diameter. Also known as throat.
charging handle
The handle of a semi-automatic or full automatic firearm used to cycle the firearm without firing. Also known as cocking handle, cocking knob or operating handle.
checkering
The diamond-shaped patterns at the fore-ends and grips of firearms made by cutting crossing lines into wood or metal with special "checkering" tools.
cheek piece
A raised portion on the side of the buttstock comb against which the shooter rests his cheek when aiming.
choke
An interior constriction at or near the muzzle end of a shotgun barrel bore that controls the pattern of shot dispersion. A shotgun barrel with no choke is called cylinder bore.
clip
A term improperly used to describe removable magazines containing cartridges. Technically, a cartridge container designed to rapidly reload the firearm's magazine. Also called the stripper clip.
cock
On early firearms such as the flintlock and percussion cap rifles, the arm-like "hammer" or device used to set the firearm into "firing" position was called the cock. It is the process by which any firing mechanism is set to be fired.
cocking handle
The handle of a semi-automatic or full automatic firearm used to cycle the firearm without firing. Also known as charging handle, cocking knob, or operating handle.
comb
The upper ridge of the stock of a rifle or shotgun where the cheek rests.
cook-off
The ignition of a cartridge by overheating.
creep
The movement of the trigger before it releases.
crimp
The inward shaping of the mouth of a cartridge case or shotshell to secure the projectile(s). Common crimps are: roll, star, fold, stab, semi-circular, split ring, and rose.
crosshairs
The sighting lines in a telescopic sight.
cylinder
The rotatable part of a revolver that contains the chambers.
cylinder gap
The maximum space between the cylinder and the barrel.
cylinder stop
A device in a revolver to stop cylinder rotation that aligns the chamber containing the cartridge to be fired with the firing pin at the rear and the barrel at the front.
Damascus barrels
An early technique for making barrels where strips or wires of iron and steel are twisted or braided in a spiral fashion and forged into a barrel. Such barrels are not strong enough to withstand the pressures of modern ammunition.
Derringer
A generic term applied to a variety of pistols that are designed to be kept in a pocket. Originally associated with small handguns designed by Henry Derringer.
detachable magazine
A large variety of removable magazines.
double action
A handgun mechanism in which a single pull of the trigger cocks and releases the hammer.
doubling
The unintentional firing of a second shot usually caused by a malfunction of the firearm.
drilling
A three-barreled gun, popular in Germany, with a rifle barrel beneath two shotgun barrels.
drum magazine
A large-capacity magazine in which cartridges are arranged in a spiral around a central wind-axis.
ejector
The mechanism that expels or throws the cartridge case free from the firearm.
ejector rod
A rod in revolvers that, when pushed rearward toward the cylinder, literally pushes or pulls the cartridge case out of the cylinder.
extractor
A hook device that pulls the case out of the chamber as the breech mechanism is opened. With firearms equipped with ejectors, the extractor brings the cartridge case to the ejector that then takes over and tosses the case from the gun.
falling block action
A single shot lever action mechanism where the "breechblock" (the part that fits securely against the cartridge keeping it snug in the breech and locks the action to allow maximum efficiency and safety during firing) slides vertically or nearly vertically to expose or lock the breech.
feed
The act of moving a live cartridge from the magazine of a firearm to the chamber.
feed ramp
The surface in the receiver or barrel of a firearm along which the cartridge rides or slides when being fed from the magazine to the chamber.
field load
A shotshell loaded for hunting small game animals and birds.
firearm
A weapon that uses gunpowder to discharge a shot.
firing pin
The part of the breech mechanism that strikes the primer of a cartridge to initiate ignition of the powder.
flintlock
The type of action of early firearms where a piece of flint stone was held by the cock and, when the trigger was pulled, the cock/flint struck the steel "frizzen" causing a shower of sparks to ignite fine gun powder in a small pan next to the "touch hole" in the barrel. The flash of the powder in the pan traveled through the touch hole and ignited the powder charge in the base of the barrel beneath the "ball" or bullet.
floor plate
A detachable metal plate at the bottom of the cartridge magazine of a bolt action rifle.
forcing cone
The tapered section at the front of a shotgun chamber where the diameter of the front end of the chamber is reduced to the diameter of the barrel bore. A forcing cone is also present in the breech end of most revolvers.
frame
The basic unit of a firearm that houses the firing and breech mechanisms and to which the barrel and stock are attached. Also called receiver.
frangible bullet
a projectile designed to disintegrate upon impact with a hard surface in order to minimize ricochet.
full choke
A highest degree of constriction that provides the tightest shot dispersal pattern at the longest distance. See also choke.
full metal jacket
A projectile with a metal jacket that encloses the entire bullet excepting the base. Also called Hardball.
fulminate of mercury
A highly sensitive explosive used as a primer compound.
gas check
A metal cup placed on the end of a lead bullet to protect it against the hot gasses of the burning powder charge.
gas port
A small hole in the barrel of a gas-operated firearm through which expanding gases escape to power the autoloading system or reduce recoil.
gas-operated
An automatic or semi-automatic firearm where the propellant gases are used to unlock the breech bolt and then to complete the cycle of extracting and ejecting.
gauge
The measure used to identify shotgun bores. It is based on the number of bore-sized lead balls equal to one pound. For example, twelve lead balls that fit the diameter of a 12 gauge shotgun equal one pound. The most common sizes of shotgun gauge are 10 gauge, 12 gauge, 16 gauge, 20 gauge, and .410. The .410 is the exception in that it is measured as a caliber not a gauge.
grip
In handguns, the grip is the handle. In rifles and shotguns, the portion of the stock to the rear of the trigger is considered the grip or wrist.
grip safety
In some handguns, such as the venerable .45 Colt semi-automatic pistol, an auxiliary locking device located on the grip prevents firing until it is depressed.
grooves
See rifling.
gunpowder
Any of various powders used in firearms as a propellant charge.
half cock
The position of the hammer when it is being retracted and held by the sear so It cannot be released by a normal pull of the trigger.
hammer
The part of the action that drives the firing pin forward.
hammer block
A safety device that separates the hammer from the firing pin except when the trigger is pulled.
hammer spur
The extension on an exposed hammer that acts as a cocking aid.
hammerless
A firearm whose hammer and striker (firing pin) are concealed within the metal frame.
handgun
A gun designed to be fired from one hand, capable of being concealed on the person and with a barrel less than 16 inches long. Until the mid-1980s the most common type was a revolver, with a rotating cylinder usually holding 6 cartridges. Since then, production of revolvers has declined and the dominant handgun has become the semi-automatic pistol, which uses a removable ammunition magazine (also called a "clip"), usually located in the handle of the gun. Each firing of the pistol forces a new cartridge up the magazine and into the chamber. A typical 9mm-caliber pistol has a magazine capacity of 8-10 cartridges.
head
The portion of the cartridge case that contains the primer, also called the base.
head space
The distance from the face of the closed breech of a firearm to the surface in the chamber on which the cartridge case seats.
high brass/high cup
Shotshells having a high metal head construction.
hinged frame action
A design where a level located on the top, side or under the frame is used to open the action. The barrel or barrels then pivot either up, down or to the side for loading or unloading. When the action is closed, the barrel(s) breech swings against the standing breech.
hollow point bullet
A bullet with a cavity in the nose to enable expansion.
improved cylinder choke
The least degree of constriction allowing a wide shot pattern. See also choke.
iron sights
A non-telescopic firearm sight. Also called metallic sights.
jacket
Layer of metal, usually copper or steel, that surrounds the lead core of a bullet..
keyhole
The elongated hole formed by an unstable bullet hitting the target sideways due to the failure to remain balanced in flight.
land & groove impression
The impression left on the bearing surface of a bullet caused by the rifling in the barrel through which it was fired.
lands
See rifling.
lever action
This is the style rifle favored by such cinematic cowboy stars as John Wayne. The lever, located below the receiver cycles the loading, firing and unloading process. It also serves as a trigger guard.
line of sight
The straight line from the eye through the sights to the target or point of aim.
loading gate
In revolvers, the hinged piece attached to the frame that is opened to permit loading. In long guns, a spring loaded cover for the loading port.
loading port
The opening in the receiver where a cartridge may be placed either directly into the chamber or into the magazine.
lock
Traditionally referred to the firing mechanism of muzzle-loading firearms as in "lock, stock, and barrel." In modern firearms, the term can refer to the firing mechanism and breech-sealing assembly or to the action of "locking" or securing the bolt of a firearm prior to firing.
locking lugs
A series or number of projections on the breech bolt designed to fit into corresponding slots in the receiver to lock the action in a closed position for firing.
lockplate
A metal plate mounted on the stock of a firearm and upon which the firing mechanism (traditionally in flintlock and percussion firearms) is attached.
lock-time
The time interval between the trigger/sear release and the firing pin striking the primer.
low brass/low cup
Shotshells with a low metal head construction.
magazine
A container for cartridges or shotshells with a spring and follower to feed cartridges into the chamber of the firearm. It may be detachable or an integral part of the firearm.
magazine floorplate
The bottom of a fixed magazine.
magazine follower
A spring-actuated device to push cartridges in a magazine to the feeding position.
magazine plug
A part inserted into a magazine to reduce its capacity. It is also the part in the end of a tubular magazine that closes the end and retains the spring.
magazine release
A device that retains or releases a detachable magazine in a firearm.
magazine safety
A safety device found on some semi-automatic handguns that prevents firing unless the magazine is inserted into the firearm.
magazine throat
A metallic insert found in some plastic magazines that aligns the next cartridge to be fed into the chamber.
magazine well
The opening in a firearm that receives the detachable magazine.
magnum cartridge
Centerfire, rimfire and shotshell ammunition that is larger, more powerful or produces higher velocities than standard calibers.
mainspring
A strong spring, aka an energy storage device, that operates the striker or hammer of a firearm.
mainspring guide
Usually a rod-like device that keeps the mainspring from kinking.
mainspring housing
A channel in which the mainspring rides.
Martini action
A hammerless single shot rifle action operated by a lever where the breechblock's movement is contained within the receiver and pivots at the rear.
match
A long cord of hemp, flax or cotton saturated with saltpeter that burns slowly without a flame. Used to ignite the early matchlock firearms.
matchlock
A firearm action of the type used by the first European explorers and Conquistadors that relies on an S-shaped (serpentine) piece of metal to hold the smoldering match. Once activated the burning end of the match, held by the upper end of the serpentine, drops to the priming powder in the pan and ignites the powder charge in the barrel though the touch hole.
metallic sights
A non-telescopic firearm sight. Also called iron sights.
mini ball
A conical shaped lead bullet with a hollow base that spreads once fired to form a tight fit between the lead of the bullet skirt and the rifle's grooves. The most popular military bullet configuration throughout the Civil War.
modified choke
Provides a shot pattern midway between full choke and improved cylinder choke. See also choke.
musket
A smoothbore military shoulder gun with a long barrel and forend stock extending nearly to the muzzle. Muskets were in common use during the 17th, 18th, and 19th centuries.
musketoon
A musket shortened for cavalry use.
muzzle
The "business end" of the firearm's barrel from which the bullet or shot emerges.
muzzle blast
The loud noise that occurs at the muzzle of a firearm when the projectile leaves the muzzle and hot gases are released into the air.
muzzle brake
A device at or in the muzzle end of the barrel (often slotted) that vents off the emerging gases behind the projectile to reduce recoil.
muzzle crown
A treatment of the mouth of the muzzle that creates an even, circular opening by shaving away metal that may be worn into a more oval pattern. Accuracy is often improved by crowning the muzzle.
muzzle energy
A bullet's energy, measured in foot pounds, as it emerges from the muzzle.
muzzle flash
The bright flash or illumination at the muzzle of the firearm that results from propellant particles emerging from the barrel behind the projectile and igniting when mixed with oxygen in the air.
muzzle loader
Any firearm that is loaded with gunpowder and projectile(s) through the muzzle end of the barrel.