Near the end of the movie Spooner, Dr. Calvin, and Sunny are in a fight with the robots at the top of the building. Spooner is holding a machine gun. Eventually, it gets knocked out of his hands and a moment later you see it hook around a bar from the strap. As you can see, it can't do this because there is no way for it to hook on, if you know what I mean. The only way for it to get the way it was would be to take the gun and slide it over from the end of the pole. In conclusion, the gun strap magically went through the bar so it could hang from it.