AK-47
The AK-47 uses gas-operated reloading.  When the bullet is moved down the barrel, a little bit of the gas behind the bullet is made to go up a small tube that pushes away the bolt.  The shooter does not have to reload by hand for every shot - the gun reloads by itself.  When you pull the trigger, the bullet in the chamber fires.  You then release and then pull the trigger again to fire another round.  When used this way, it is called a semi-automatic firearm.  A few AK-47's are made to be used only this way but most are fully automatic firearms.