The scene called for dummy rounds, not blanks or an empty cylinder.
An accentual discharge could occur if one’s finger was on the trigger while cocking the hammer back. If Baldwin was practicing fast-draw, fast shooting, I suppose he have done that. But it was a rehearsal. No need for anything to be in the gun.
It is quite easy to see if a revolver is loaded with blanks or real rounds. The nose of a blank looks nothing like the nose of a real round. Just spin the cylinder while looking at the holes!
Dummy rounds may be a bit more difficult but not impossible.
Agreed, Baldwin was probably cocking the hammer while drawing, with his finger on the trigger. Or possibly using the palm of his off hand.
Yes, why did it even have blanks in it if he was practicing drawing? Presumably those revolvers are not that easy to fire accidentally, but he managed by accident and trying to avoid pointing it at anyone for the bullet to go through one person’s chest and seriously injure another?
They also presumably knew that weapons were usually provided by the armorer, at least in their experience in many other productions. Therefore, why did they accept them without her there? Then the assistant director apparently called out “cold gun” despite that and without checking it.