I saw that shotgun shot, he then puts a real round in and makes a hole, but the side window I feel he just knocked out with the gun.  Why are all the bodies piled up in a corner when he walks in? Dummies set up with some actors mixed in making noises.  Watch the reactions when they are hit.  There is also a real bullet magazine taped to the side, always in camera shot, I think he puts it in by accident when reloading and then clears the chamber and puts in rubbers around 7:40 or so.