FIREARMS GLOSSARY

FIREARMS GLOSSARY

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.



ammunition


The projectiles fired from guns. The term also includes the fuses, propelling charges, or primers of the projectiles.


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.


BB ammunition


In Shotgun shells, BB shot has a diameter of .180 inches. For use in airguns, a BB is .175 inches in diameter.



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.

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.

breech

The rear of the barrel into which the cartridge or propellant is inserted. Also called chamber.



breech face


That part of the breechblock or breech bolt against which the head of the cartridge case or shotshell rests during firing.


buckshot


Large lead pellets ranging in size from .20 inches to .36 inches in diameter used in shotshells.


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.

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.

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.

thingy


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 thingy. It is the process by which any firing mechanism is set to be fired.


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.

double action


A handgun mechanism in which a single pull of the trigger thingys and releases the hammer.

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.


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.



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.


floor plate


A detachable metal plate at the bottom of the cartridge magazine of a bolt action rifle.

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 metal jacket


A projectile with a metal jacket that encloses the entire bullet excepting the base. Also called Hardball.

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.


half thingy

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 thingying aid.

hammerless


A firearm whose hammer and striker (firing pin) are concealed within the metal frame.


hollow point bullet


A bullet with a cavity in the nose to enable expansion.


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.


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.

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.


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.

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.

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.

muzzle velocity


The velocity of a projectile as it exits the muzzle of a firearm.


open bolt system


A firing system for automatic and semi-automatic firearms where the bolt remains in the rearward position after each cartridge is fired or when firing is stopped. The firing pin is generally in a fixed position in the bolt. This system allows for faster cooling of the action. This system works in a manner exactly opposite to tht of the closed bolt system familiar to most shooters. Therefore, care must be taken with an open bolt firearm as natural, but, in this case, wrong tendency of "closing the bolt" fires the cartridge.

open sight


A non-telescopic sight. Metallic or Iron sight.

operating handle


The handle of a semi-automatic or full automatic firearm used to cycle the firearm without firing. Also known as charging handle, thingying handle or thingying knob.

operating rod


A long rod extending from the gas piston that may be attached to a thingying knob or handle.

optical sight


Usually a telescopic sight but also includes laser sights.

out of battery


The condition where the breeching mechanism is not in proper position for firing.

patch


A piece of leather or cloth, greased and placed around the bullet (round ball) before using the ram rod to push it down the barrel of a muzzle loader to its final seat on the powder charge. Also a piece of paper wrapped around a lead bullet to prevent leading of the barrel or improve the gas seal. Also a piece of cloth used to clean the bore of a firearm.


point of aim


The place or point on a target that intersects the straight line generated by the alignment of the front and rear sights of a firearm.

point of impact


The point at which a projectile hits the target.

pressure


The force developed by the expanding gases generated by the combustion of the propellant and exerted against the cartridge case, base of the bullet, chamber and bolt face.

pressure barrel


A heavy-walled barrel fitted with instrumentation to measure pressure.

primer


The ignition component of a cartridge.


pump action


This action uses manual action on a moveable forearm, parallel to the barrel. Sliding the forearm to the rear opens the action and empties the breech or chamber by extracting and ejecting the empty cartridge case. Sliding the forearm forward loads a new cartridge into the chamber and locks the action for firing. Also called slide action.

Quaker gun


An imitation gun usually fashioned from wood.

ramrod


A wood or metal rod used to force the wad and bullet down the barrel of a muzzle-loading firearm.

rate of twist


The distance required for the rifling to complete one revolution. For example 1 turn in 12 inches.

receiver


The basic unit of a firearm that houses the firing and breech mechanisms and to which the barrel and stock are attached. Also called frame.

receiver ring


The part of the receiver that is threaded in order for the barrel to be attached to it.

recoil/Muzzle Flip


The rearward or opposite force or movement of a firearm caused by and equal to the force the firing or moving the projectile forward. Commonly called kick and measured in foot pounds.

recoil shield


On a revolver, the recoil shield is the metal extensions on the firearm's frame that cover the exposed back of the cylinder on either side of the gun. It is designed to prevent fired or unfired cartridges from sliding out of the cylinder and to protect the exposed primers of cartridges in the chambers on either side.

recoil spring


The spring that returns a semi-automatic or automatic firearm to battery.

reload


A cartridge that has been reassembled with a new primer, powder, and projectile.

revolver


A firearm with a cylinder containing several chambers. The cylinder rotates around an axis allowing each cartridge to be fired by the same firing mechanism.

rib


A raised surface, either solid or ventilated, running along the top of a barrel and used as a sighting plane.

ricochet


The deflection of a projectile after impact.

rifling


Helical or spiral grooves cut into the inside of the barrel surface to cause the bullet to spin in a rotary or spiraling motion causing the projectile to travel with greater stability. The cut-away portions of the rifling are called grooves while the uncut portions are called lands.

rimfire cartridge


A flange-headed cartridge containing the priming mixture inside the rim cavity.

rimless cartridge case


A centerfire cartridge case with the case head of the same diameter as the body.

rimmed cartridge case


A cartridge case with a base or head larger in diameter than the body of the case.

rolling block action


A single-shot action where the breechblock and hammer are swung rearward, away from the barrel breech to load or unload the firearm. When closed, the breechblock locks the cartridge in place ready to be fired.

safety


A device on a firearm designed to prevent accidental firing.

sear


The part of a firearm that retains the hammer or striker in the thingyed position until the trigger is pulled.

selector


In a double-barreled firearm, the selector is a device to allow the shooter to choose the barrel used by the first pull of the trigger. In full automatic firearms, it is the lever that chooses between semi-automatic and automatic firing and between a high and low rate of automatic firing.

semi-automatic


A repeating firearm that requires a separate pull of the trigger for each shot fired. The energy of the discharge is used to cycle the process of extracting the empty cartridge case and loading and locking in place a new cartridge ready to be fired by the next trigger pull. Compare automatic.

serial number


A unique number applied to a firearm in order to identify the individual firearm.

shot


Spherical pellets used in loading shotshells or cartridges.

shotshell


The fixed ammunition for a shotgun composed of a brass head, a plastic or paper shell, a primer, powder or propellant, a measure of shot, and various wads or thin card-like discs over the shot, under the shot and over the powder. A combination wad made of plastic is used in many modern shotshells to act as a spacer, shot protector and over powder wad.


sidelock action

In this design, the firing mechanism is attached to a side plate rather than being an integral part of the frame.

sight


Any of a variety of devices, mechanical and optical, designed to assist in the aiming of a firearm.

sleeve

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 barrel liner.

slide action


This action uses manual action on a moveable forearm, parallel to the barrel. Sliding the forearm to the rear opens the action and empties the breech or chamber by extracting and ejecting the empty cartridge case. Sliding the forearm forward loads a new cartridge into the chamber and locks the action for firing. Also called pump action.

smallbore


Generally refers to a .22 caliber firearm.

smokeless powders


Propellant containing mainly nitrocellulose or both nitrocellulose and nitroglycerine.

smoothbore


Firearm with unrifled bore.

spitzer bullet


A bullet with a sharp point, long ogive.

staggered column magazine


A box magazine that has two staggered columns of cartridges that increase capacity but not length of the magazine.

stock


A component, traditionally wood but also made of laminates and other weather resistant materials, to which a barreled action is attached to enable a shooter to hold the firearm.

stripper clip


See clip.

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 chamber throat.

toe


The bottom part of the butt of a rifle or shotgun.

top strap


The portion of a solid frame revolver that passes over the cylinder.

trajectory


The curved path of a projectile from muzzle to target.



trigger


The part of a firearm that is moved manually to cause the firing pin to be released by the sear, the cartridge primer struck, the propellant ignited and the projectile sent on its way.

trigger guard


A rigid loop around the trigger that prevents accidental discharge or damage to it.

trigger pull


The amount of force that must be applied to the trigger of a firearm to cause the sear release.

tubular magazine


A tube-shaped magazine in which cartridges or shotshells are arranged end-to-end. It may be located under the barrel or in the butt stock.

unload


Remove ammunition from a firearm.

velocity


The speed of a projectile at a given point along its trajectory.

wadcutter bullet


A cylindrical bullet having a sharp shouldered nose intended to cut target paper cleanly to facilitate easy and accurate scoring.

wheel-lock


An early type of firearm mechanism where a wheel with serrated edges is wound against the tension of a strong spring and spins against a piece of iron pyrite causing a shower of sparks into the pan to ignite the charge.

windage


The lateral drift of the bullet in flight caused by wind.

zero


Sight adjustment so the bullet will strike the target at the point of aim.