Bump firing is a way of firing a semi-auto rifle or in this case a shotgun VERY fast. Basically you hold the firearm so that the recoil of firing will cause your finger to come off the trigger long enough for the trigger to reset and the action to close on a live round.
You also have your off hand (left hand for right handed people) pulling forward on the firearm, you generally hook your trigger finger through the trigger guard in front of the trigger to the loop of your pants. When you pull froward with your left hand the firearm fires and recoils back since you are still pulling, the firearm continues to fire over and over.
A lot of fun but a big waste of ammo.
I can try to video tape bump firing a saiga 20 tomorrow, depending on if we get the pit done.