Would he have checked the gun if it was a scene that required him to shoot himself in the head? Or one of his children? Can you think of any other situation in life in which the guy who pulls the trigger is not charged? For example a friend hands me a gun and says it’s not loaded. I point at him and shoot it, and it is loaded? He dies, I’m charged plain and simple.
Does every actor check guns for live rounds? I don’t know the answer but I’m guessing I’ve worked on about as movie sets as you have.