Revealing mistake: When Kersey tries to shoot Wilson at the hospital, he lifts up the table to knock his gun away from him. Kersey fires a shot at the table when it moves up, but a hole doesn't appear in the table. This indicates the gun was loaded with blanks (obviously) and no other effects were done for the scene.
Revealing mistake: During the final fight sequence between Paul Kersey and Nirvana at the hospital, at one point you can see that Kersey is not Charles Bronson but his stunt double.
