Ok, follow me on this one. In the movie, think about the bullets. Hopkins went to the hotel room to switch guns. The police's gun was most likely loaded, Hopkins must have replaced it with an empty gun because 4 of the casings were missing out of the pack. The police officer would have realized it was empty. I have thought about so many different ways it would have worked, please let me know if you have a logical, plausible explanation for how the bullet math works.