Other articles said that the crew had been using that gun with live ammo for target practice some time prior; that even a fragment of a live shell in the chamber can injure or kill if the gun is loaded with a blank and fired at close range; that the regular union armorer crew had walked off an hour earlier due to safety issues; and that the live ammo was stored in the same location as the blanks.
I imagine the union people are having mixed emotions right now:
1) Glad it wasn't us and we left, since that arrogant ahole wouldn't let us do our job properly.
2) If only we had been there, this woudn't have happened.
Add 3) I hope no one finds out we put live ammo in it to make a union statement.