Revealing mistake: When Bruce Wayne is heading to the hearing at the courthouse, he checks his revolver to make sure it's loaded. His intent is to execute Joe Chill for killing his parents, so he would need a working gun. But when he opens the cylinder of the revolver to make sure it's loaded, you can see that all of the bullets have had the primer removed (the end of each bullet casing has a hole in it.) This is done to make each round impossible to fire, for safety on the set.
Picture added by bret konsdorf