I remember one question in the California gun safety exam asked what next step was after someone clears a gun, shows you an empty gun, and hands it to you. If you didn't say that you checked the gun yourself you got it wrong.
From what I've read since the event happened, AB's gun in this case was
not supposed to be an empty gun. It was supposed to be loaded with inert
dummy rounds - that look real unless you look very closely.
The only purpose of loading a revolver in a movie with dummy rounds is so that the bullets in the cylinder would be visible in the camera when you point the gun at the camera. And when pointing a single-action gun at the camera in a threatening manner, the hammer was probably supposed to be ****** as well.
From what I understand from reading about them, is that the only visual difference between such a dummy round and a real one is that the dummy has a hole on the
side. So, to be able to check the gun for a real round among the dummy rounds, the actor would have to remove each round, look at it from multiple angles and put it back in again.
On the Colt 45, that would have involved a procedure of cocking the gun (or half-cock?), opening the loading gate and for each round, one at a time, rotate the cylinder and push the round out with the ejection rod, inspect it (in the low light inside the church) and put it back again.
If AB would have done that on the set — after two people supposedly had already checked the gun — I'd think that the director, the AD, and the camerawoman herself wearing a heavy steadicam rig on her shoulders would have got quite annoyed at him.