there shouldn't even have been live ammo on the set. According to the armorer, she locked up the guns, but the ammo was just lying around, including live ammo.
There is more than one report that the crew used the set weapons for target shooting, including the very day they were working on the scene where Ms. Hutchins was shot. The armorer said that she loaded the gun. Did she load it with live ammo for the crew to shoot with, or did someone take the gun and reload it? Or did she remove the live ammo and reload it for the scene, and left a live round inside?
This production hired not one, but two persons in roles with responsibility for the set firearms, who had gotten in trouble for misuse of set firearms on other productions.