CNN CNN Newsroom February 10, 2014 14:22:00
>> when the gun is fired the explosion occurs. that is what the pressure buildup pushes the bullet out of the muzzle. and that will travel in the forward direction. the cartridge case -- if the gun is pointing that way the bullet will go that way. the cartridge case stays inside the gun and it is forced in the opposite direction. the bullet goes that way and cartridge case slams against the inside of the gun providing momentum to automatically cycle the gun. it will slam against inside surfaces ...
Source: archive.org