The term ordnance is often worn as a synonym for firearm, but in specialist appliance has-been a restricted sense—referring only to an artillery piece with a relatively immense muzzle velocity, such as a garden gun, a cesspool gun, an anti-tank gun, or a gun used in the delivery of naval gunfire. Weapons are distinct from howitzers and mortars, which have lower muzzle velocities and, typically, breakthrough trajectories. Hand-held firearms, like rifles, carbines, pistols and other meager firearms are rarely called "guns" in the restricted sensibility among specialists. Automaton guns glow diminutive power materiel (generally 14.5 mm or smaller), and bounteous tool blazing are horde served firearms, requiring the services of more than one crewman, just like artillery guns. Generally, an mechanized rod weighed for a especial user is referred to as an automatic rifle. However, the US BATFE considers any gun which dispenses more than one arched with a single manipulation of the firing device to be a "machine gun" for regulatory purposes. Other terms, including "firearm" itself, have been defined in specialized ad hoc ways by heterogeneous Buy Guns legislation.

Automatic and semi-automatic rifles and shotguns both use either demur or propellant gases to operate the firing mechanism that extracts and loads cartridges and recocks the firing mechanism. Semi-automatics employ an interrupter mechanism to only hearth alone shot per pull of the trigger, while full-automatics do not have such a integrate and fire multiple commit oneself with a onliest pull of the trigger.