Another quality prop from Riddick. This is the firing version. It uses 2 9V batteries in each side of the gun, this supplies power to small charges or 'squibs' at the front of the gun via the rotory controller switch on the top of each rifle. Each barrel can hold 5 squibs that just push into small connector holes near the ends of the barrels.
This screenshot clearly shows the ring of charges in the end of the barrels.