Machine Gun is a firearm that fully automates bullets in speedy succession from an ammunition belt or magazine, typically at a powerful rate of fire at least 300 to 1800 rounds per minute, and can be used in either mounted or portable position. Not all fully-automatic firearms are machine guns but sub-machine guns, rifles, assault rifles, shotguns, pistols or cannons may be capable of fully automatic fire; not designed for sustained fire. As a class of military rapid-fire guns, true machine guns are fully automatic weapons designed to be used as support weapons and generally used when attached to a mount or fired from the ground on a bi-pod or tripod. Many machine guns also use belt feeding and open bolt operation. However, some of the features are not normally found on rifles.