In the safe opening scene, Kevin Dillon's pistol alternates between the slide being forward and the slide being locked back- hence, empty.
After HSI guard Mike shoots the lobby guard 3 times in the upper body/head area, dragging his body, there is no blood or trail which would have been instantaneous.
At 78 minutes, when Rosa is forcing Shane to open the safe, the exact same shot of Kevin Dillon saying "Come on" while pointing a gun is used twice. This is made particularly obvious by how the way Rosa is holding the gun immediately changes in the subsequent shot after the second "Come on".
When Bruce Willis and Kevin Dillon are arming themselves, Kevin looks down and states there's 8 shotgun rounds in the box- but the box he's looking into clearly reads "CO2" containers- commonly used to power BB-guns.