A machine gun is in most cases a portable assault rifle that is capable of firing hundreds of rounds, or bullets, a minute. A modern assault rifle has the option of firing in single shot and fully automatic bursts. But how does it achieve this?
First we must look at the process of how a rifle fires a single round. This will be described in a step by step process and it is already assumed a loaded magazine is fitted to the weapon.
1. Pulling the cocking lever back moves the breech block back over the rounds in the magazine. At the same time it pushes the hammer back into a postion where it is held in place by the trigger sear. A spring creates tension on the breech block so that when the cocking lever is released the breech block is forced forwards under its own force.
2. As the cocking lever is released the breech block moves forward and grabs the edge of a round. The round which is under pressure from the magazine spring is forced into the chamber.
3. The rifle is now ready to fire, all that is required is to ensure the safety is off and squeeze the trigger.
4. Releasing the safety mechanism enables the trigger mechanism to be operated. On squeezing the trigger, the hammer is released and strikes the end of the firing pin which is located centrally within the breech block.
5. The firing pin is forced forward and strikes the percussion cap at the base of the round.
6. The percussion cap causes a small charge to go off which ignites the charge in the body of the round. This resultant explosion causes the resultant force which fires the head of the round out of the barrel and towards the target.
7. As the round and explosive gases pass down the barrel some of the gases are diverted through a small hole to force back the breech block against its spring, resetting the hammer and pushing a round into the chamber as it forced forward again under pressure. This readies the weapon for the next shot.
Now we have described the process of a single shot it is relatively simple to understand the automatic firing of the weapon. In single shot mode we have seen that the hammer is reset, waiting for another pull on the trigger. In fully automatic mode the hammer is not held in position by the trigger sear after firing. In this situation, as long as the trigger is depressed, the hammer is allowed to repeatedly strike the firing pin allowing as many rounds in the magazine to be fired in one burst.
