 FACT: SPOILER: There was no reason to have the criminal assemble and  disassemble the submachine gun as he does twice in the film. The  weapon sans magazine with the stock folded would have fit  comfortably in the piece of luggage he was toting around. Also, when  he is shooting the entire bus at the beginning, there is no muzzle  climb to the weapon, as there would be in reality. To be really  picky, it would have been impossible for him to have shot so many  people through the seats at the front of the bus, including the  driver, with a 9mm weapon without hitting seat springs and other  items. More of the victims should have survived their wounding,  also. A fully automatic weapon is not magic, regardless of any  guesses to the contrary.