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. Machine guns fire bullets delivered from a long chain called an ammunition ('ammo') belt, or use spring-loaded boxes called magazines. Machine guns are divided into heavy-duty machine guns, and sub-machine guns.
Heavy machine guns (HMG) are placed on the ground and supported on a tripod, or on a vehicle. The vehicle would have a support for the gun with a rotating base or turret. Some heavy machine guns need two men to operate it, one to assist with loading ammunition, and one to aim and fire. It always takes two men to carry one.
Many heavy machine guns, such as the Browning M2 .50 caliber machine gun, are exact enough to hit things that are very far away. During the Vietnam War, Carlos Hathcock shot at 7382 ft (2250 m) with a .50 caliber heavy machine gun to which he had connected a telescope.
- Henderson, Charles. Marine Sniper Berkley Caliber. (2005) ISBN 0-425-10355-2.