Autocannon

An autocannon or automatic cannon is a rapid-fire projectile weapon firing a shell as opposed to the bullet fired by a machine gun. Autocannons often have a larger caliber than a machine gun (i.e., 20 mm or greater). Usually, autocannons are smaller than a field gun or other artillery, and are mechanically loaded for a faster rate of fire. They can use a variety of ammunition: common shells include high-explosive dual-purpose types (HEDP), any variety of armour-piercing (AP) types, such as composite rigid (APCR) or discarding sabot types (APDS).

Although capable of generating a high rate of fire, autocannons overheat if used for sustained fire, and are limited by the amount of ammunition that can be carried by the weapons systems mounting them. Both the U.S. 25 mm Bushmaster and the British 30 mm Rarden have relatively slow rates of fire so as not to use ammunition too fast. The rate of fire of a modern autocannon ranges from 90 rounds per minute (British RARDEN) to 2,500 rounds per minute (GIAT 30). Systems with multiple barrels can have rates of fire over 9,000 (GSh-6-23) rounds per minute. Such extremely high rates of fire are effectively employed by aircraft in air-to-air combat, where the target dwell time is short and weapons are typically operated in brief bursts.