The Replacement Killers

Corrected entry: In the arcade shootout, one of the replacement killers' Heckler & Koch MP5K suddenly switches to a full-size MP5N between shots.

Correction: If you watch him after he takes the MP5K out of the case, he starts walking down the aisle by the photo booth and pulls back the right side of his trench coat, grabbing a full-size MP5N that his hanging from his right shoulder.