I think this^^^ attorney is incorrect and may be purposely muddying the waters when saying it was not the AD's responsibility to check the gun. Here is what a firearms specialist with 30 years of film experience says:
On film sets, the person most responsible for safety is usually the First Assistant Director, and as a result they will also inspect the firearm -- a task the director, producer, camera operator or cinematographer may oversee, too.
Every single person on set -- cast or crew -- has the right to inspect a prop gun. But the specialist is the only person who will hand the firearm to an actor for use, and the specialist is the same person who receives it back when the talent is done.
WHAT ARE THE RULES FOR FIREARMS ON SET?
The weapons master is required to be on set whenever a weapon is being used. The Actors' Equity Association's guidelines state that, “Before each use, make sure the gun has been test-fired off stage and then ask to test fire it yourself. Watch the prop master check the cylinders and barrel to be sure no foreign object or dummy bullet has become lodged inside."
Further, “All loading of firearms must be done by the property master, armorer or experienced persons working under their direct supervision.”
Opinion: Guns can be safely used on a film set -- but only if you follow the rules - CNN