Revealing mistake: When trying to take the warehouse, we see a German machine gun position in a lower window. Pay close attention to the brickwork below the window. There are several marks visible that all end up with a bullet hole in the middle of them, hiding the charge for the effect. (00:14:30)
Revealing mistake: When the first tank comes during the final battle, look carefully at the German sitting on it and you will see that he's actually a dummy.
Answer: That actually is the clip. It is loaded into the top of the rifle, and is ejected with the last round. See http://www.wwiitech.net/main/usa/weapons/m1/.
J I Cohen