A machine gun basically works by utilizing the recoil of the bullet that is being fired to take care of all the other operations that are required to be done before the next bullet can be fired. These include removing the spent cartridge of the bullet just shot, putting in the new bullet cartridge, pulling the bolt and finally pressing the trigger.

Energy that was being wasted in a conventional gun is utilized in a machine gun to automate all the operations and allow the person with the machine gun to shoot continuously till the ammunition for the gun lasts.

If you know, pls tell
difference between sniper & machine gun