structural failure. All firearms, whether they are semi-automatic, fully automatic, or otherwise, will overheat and fail if fired indefinitely. This issue tends to present itself primarily with fully automatic fire. For example, the MG34 may have a calculated cyclic rate of 1200 rounds per minute, but is likely to overheat and fail in the space of one minute of continuous fire. Semi-automatic firearms may also overheat if continuously fired. Recoil plays a significant role in the time it takes to reacquire one's sight picture, ultimately reducing the effective rate of fire. Automatic firearm types Automatic firearms can be divided into six main categories: Automatic rifle The standard type of service rifles in most modern militaries, usually capable of selective fire. Assault rifles are a specific type of select-fire rifle chambered in an intermediate cartridge and fed via a high-capacity detachable magazine. Battle rifles are similar, but chambered in a full-powered cartridge. Automatic shotgun A type of combat shotgun capable of firing shotgun shells automatically, usually also semi-automatically. Machine gun A large group of heavier firearms used for suppressive automatic fire of rifle cartridges, usually attached to a mount or supported by a bipod. Depending on size, weight and role, machine guns are divided into heavy, medium or light machine guns. The ammunition is often belt-fed. Submachine gun An automatic, short rifle (carbine) typically chambered for pistol cartridges. Today seldom used in military contexts due to a rise in the use of body armor, they are commonly used by police forces and close protection units in many parts of the world. Personal defense weapon A new breed of automatic firearms that combines the light weight and size of the submachine gun with the medium power caliber ammunition of the rifle, thus in practice creating a submachine gun with body armor penetration capability. Machine pistol A handgun-style firearm, capable of fully automatic or burst fire. They are sometimes equipped with a foldable shoulder stock, to promote accuracy during automatic fire, creating similarities to their submachine gun counterparts. Some machine pistols are shaped similarly to semi-automatics (e.g., the Glock 18, Beretta 93R). As with SMGs, machine pistols fire pistol caliber cartridges (such as the 9mm, .40, .45 ACP etc.). Burst mode Burst mode is an automatic fire mode that limits the number of rounds fired with each trigger pull, most often to three rounds. After the burst is fired, the firearm will not