One of several dozen safety violations by the crew.
Prop weapons are supposed to be unloaded during a rehersal which state is supposed to be personally verified by the Armorer immediately before any activity.
Weapons should only be loaded (with blanks) by the Armorer, and only immediately before filming begins. They are supposed to be unloaded and cleared immediately afterwards.
All weapons and ammunition are supposed to be under direct personal control of the Armorer, and stored in a secured location when not in use for filming and rehearsal.
There was no reason to permit live ammunition anywhere on this set.
The list of violations goes on to the point of tedium. And there had been at least two previous negligent discharges of firearms on that set.
Baldwin, as Producer is ultimately responsible for the negligent lack of industry-standard safety procedures, announced and enforced, and the death that resulted.
I would also add the AD, Halls, as a responsible party. I have read or listened to several directors and actors who have cited ADs as the go-between from armorer to actor who should personally show the actor the condition of the gun or call over the armorer to show the actor. It shouldn't ever be an "I say so" or an "I was told" situation.
IMO all three, the armorer, the AD and the actor/producer, Baldwin, were negligent and none of them have any excuses at all.