Corrected entry: In the scene where the Van is rolling, whilst Arthur is about to fight the black security guard with the gun, he forces the gun out of his hand as he gets it out and it is left further down the corridor. Next when they slide into the room the gun slides in with them through the door even though it was dropped much further up the corridor.
nbafanscw
27th Jan 2011
Correction: Actually, there are two guns in the hallway; when Arthur goes to hide, he pulls out a gun but is disarmed, when he and the black guy are fighting you can actually see both guns for a brief second. Obviously the second gun is closer than it should be, but I think Arthur's gun is the one that enters the room with them.
nbafanscw