If AB goes for a jury trial, he better hope for people who have had zero experience with guns. It seems to me that his defense will be to blame others.
Any one who has had guns, the first rule, is to treat every gun like it is loaded with live ammo, and when someone hands you a gun, they open it, if there is a bullet in it, check it to see if it is a live round or dummy round. The one holding the gun, is 100% responsible. And never point a gun at someone, and pull the trigger.
That information is so basic. If AB has ever signed any documents on gun safety, stating that he is aware of the rules of gun safety, he is toast. And he has been on so many sets with guns, including this one, I bet he has just signed it, not paying attention.