Live rounds should have never even been on set like that. The prop master, armorer or who evers job it was to check the weapon failed criminally negligently.
Who half a$$ed their job so bad that they didn’t verify the gun was loaded with deadly ammo and just handed it off and said yeah yeah cold gun it’s safe. Did somebody lie on their resume about their experience? That’s insane criminal laziness and stupidity or possibly just plane murder. I hope this is investigated properly; this is not a no fault situation.