Automatic firearm

An automatic firearm uses energy from firing to cycle its action and continues firing while its trigger remains depressed, until the trigger is released or ammunition is exhausted.

Firearm action: The mechanism that loads, fires, extracts, and ejects cartridges in a firearm. Automatic fire depends on an action that repeats these operations after each shot.
Semi-automatic firearm: A firearm that fires one shot per trigger pull and automatically reloads the chamber for the next shot. It cycles automatically but requires a separate trigger pull for every shot.
Cartridge (firearms): A unit of ammunition containing a case, primer, propellant, and projectile or projectiles. Each firing cycle consumes a cartridge and chambers another from the supply.
Light machine gun: A portable machine gun intended to provide automatic fire for a small infantry unit. It applies automatic fire in a mobile squad-support role.
Maxim gun: An early recoil-operated machine gun developed by Hiram Maxim in the late nineteenth century. It demonstrated how firing energy could power sustained automatic operation.
Recoil operation: A firearm operating system that uses rearward movement of the barrel or bolt caused by firing to cycle the action. Some automatic firearms use recoil to power each loading and firing cycle.
Selective-fire firearm: A firearm with a selector that allows the user to choose among firing modes, commonly including semiautomatic and automatic fire. Its automatic mode shares the defining repeated-fire behavior, while its selector adds alternatives.
Chamber (firearms): The part of a firearm that holds a cartridge in position for firing. The action must place each successive cartridge in the chamber.
Heavy machine gun: A machine gun designed for heavier ammunition and usually mounted or crew-served operation. Its greater size and ammunition support sustained or long-range fire.
Hiram Maxim: An American-born inventor whose Maxim gun became an influential early machine gun. His design helped establish practical recoil-powered automatic firing.

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