Glossary of firearms terms

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Accelerator
A device used in an automatic or semiautomatic firearm to increase the speed of the boltís rearward travel by the application of leverage at the critical point of travel.

Accessory
Any article used with but not an integral part of the weapon. Oiler, sling etc.

Action
The assembly of moving parts that feed the cartridge into the chamber, lock and seal the chamber, fire the cartridge, unlock the chamber, extract and eject the empty cartridge case.

Action, blowback
In an automatic or semiautomatic firearm, an action having no mechanical locking system. At the moment of firing the force of the recoil spring combines with the weight of the hammer, slide and other moving parts to hold the breech closed. The weight of these parts exceeds the weight of the bullet to such an extent that the expanding gases discharge the bullet from the barrel before the inertia of the breech action is overcome. Then residual pressure blows the breechblock action open.

Action, blow-forward
In an automatic or semiautomatic firearm, the barrel is blown forward to open the action and eject the empty cartridge case. A powerful spring then forces the barrel rearward against the standing breech. As the barrel is forced back the gun is cocked and reloaded.

Action, bolt
The breech closure is achieved by longitudinal movement of the breechblock parallel to the axis of the bore. Types include turn-bolt action, straight pull action, camming-lug bolt and wedge-type bolt.

Action, double
1 Firing mechanism in a revolver in which a continuous pull on the trigger will revolve the cylinder to place a cartridge in the firing position, cock and then release the hammer to fire the gun. Afterwards the trigger must be released before the cycle can be repeated. Most double action arms can also be cocked manually by moving the hammer to full cock position.
2 In some autoloading pistols, a mechanism by means of which continuous pressure on the trigger cocks then releases the hammer to fire the first shot.

Action, drop block
An action, generally lever operated, in which the breechblock moves vertically in grooves in the sides of the receiver walls.

Action, falling block
Lever operated action in which the breechblock is pivoted at the rear of the receiver so that the face of the breechblock swings below the chamber to open the action.

Action, hinged frame
An action using a standing breech and one or more barrels so hinged to the receiver that when the action is unlocked the muzzle swings up or down for the purpose of extraction and loading.

Action, lever
Breech closure is actuated by a lever linked to the breechblock in a manner that provides the desired opening and closing action. Usually the lever is so mounted under the receiver that it forms a trigger guard and extends rearward along the small of the stock or pistol grip.

Action, pump see Action, slide

Action, recoil-operated
An action in an automatic or semiautomatic firearm where the breechblock and barrel are locked together at the instant of firing. When the bullet is discharged the pressure of the gas starts to move the locked bolt and barrel rearward, the barrel strikes a stop that withdraws its locking device from the breechblock, slide or bolt, which in turn continues rearward to eject the fired case and prepare for the reloading motion. In short recoil weapons the barrel and breech are locked together for less than three quarters of an inch (20mm) of travel. In long recoil weapons the breech and barrel remain locked for the full distance of the recoil stroke, the barrel is then unlocked and thrust forward while the bolt is retained to eject the case and reload the chamber.

Action, rolling-block
An action, generally lever operated, in which the breechblock is made to rotate downward and backward from the chamber about an axis pin.

Action, single
An action that requires manual cocking of the hammer before pressure on the trigger will fire the weapon.

Action, slide
Breech closure is accomplished by means of an operating rod attached to the fore-end and linked to the breechblock. The operating rod is moved forward and backward along guides parallel to the barrel to provide the desired opening and closing action.

Action, straight pull
A type of bolt action where the rotary motion required to engage or disengage the locking lugs from their locking recesses is applied by the action of studs sliding in helical grooves contained on the inside surface of the bolt sleeve cylinder.

Action, turn bolt
A type of bolt action in which the action is locked by turning one or more locking lugs into recesses cut into the receiver.

Action, wedge type bolt
A type of bolt action employing a ramp or cam assembly to raise, lower or move latitudinally the bolt end to wedge it against a supporting surface in the receiver, thereby locking the action.

Adapter
A device intended to alter the use or functioning of a gun to permit practice with smaller, less expensive ammunition. Sometimes called a subcalibre tube with the Morris tube being a well known example.

Ammunition
Consists of the bullet or projectile, the propellant, the igniter or primer and the case. The current term for small-arms usage is cartridge.

Anvil
Fixed metal point against which the firing pin or striker compresses the primer mixture to cause an explosion. In the Berdan primer the anvil occurs in the head of the cartridge case, forming a projection in the centre of the primer pocket. In the Boxer primer the anvil occurs as a small arbor of metal rigidly fixed over the explosive pellet across the primer cup. In rim fire cartridges the anvil is formed by either the rear face of the barrel or cylinder serving as a resting place for the rim of the cartridge.

Aperture sight see Sight

Armory
1 A place where weapons are manufactured.
2 A place where weapons are stored or displayed.

Arsenal
A place where ammunition is manufactured.

Assembly
Any collection of mutually operating parts housed together to form a single unit.

Autoloading
Any of a variety of arms which upon being manually loaded and fired, will eject the fired case, load the next cartridge from the magazine and cock the gun ready for refiring. Pressure on the trigger must be released and reapplied after each shot for the next shot to fire. Gas expansion, recoil and mechanical spring action are used to perform ejection and reloading operations. Also called semi-automatic or self-loading.

Automatic
Any of a variety of weapons using gas pressure, recoil, etc., after the first shot is fired to eject the fired case, load the next cartridge from the magazine, fire and eject that cartridge, and repeat the process continuously until ammunition is exhausted or pressure on the trigger is released. The term is often misapplied to autoloading actions.

Axis
The central line of the bore, perpendicular to a plane passing through the muzzle.