A machine gun is a weapon that can fire one bullet after another as long as the trigger is pulled and there are bullets ready to fire. This is called automatic fire. A more general name for this type of weapon is an automatic weapon. Machine guns fire bullets delivered from a long chain of cartridges called an ammunition ('ammo') "belt", or use spring-loaded boxes called "magazines". Machine guns are usually divided into heavy-duty machine guns, light machine guns, and sub-machine guns.