I'm picking up a bit of a disconnect here between regular gun guys and guys who know how the movie industry works.
Summary of my understanding so far....
Live gun/ammo in the real world = projectile
Live gun/ammo in movies = blank
Real world = treat all guns like they gonna put a hole in something.
Movies = there's a difference between a "live" gun and a "prop" gun that may look real (even going as far as appearing to contain ammunition) and make clicks but is incapable of accepting and firing ammunition.
I suppose the question really is was this an negligent discharge or a mechanical/systemic failure?
1) If the gun was pointed in the correct direction and a bang was expected to happen then has the actor actually done anything wrong?
2) If the actor was supposed to be handed a "prop" (refer to above definition) pointed it in the correct direction and pulled the trigger as instructed and a bang happens is it the actor's fault, the prop guy's or a systemic failure that led to the actor being handed a live weapon instead of a prop?
3) The actor is randomly waving a known "prop" gun about and said weapon fires?
4) The actor is randomly waving a known "live" gun about and said weapon fires?
Answers IMO
1) No. The failure is either mechanical of the gun itself ie BFA plug coming loose and turning into a projectile, maintenance related ie there's a squib from previous use that hasn't been cleared or someone loaded the weapon with real ammo instead of blanks.
2) Maybe. If the full chain of custody has been followed and the actor has been incorrectly handed a live weapon then no, the fault is elsewhere. The chain of custody has been broken ie at the directors request then partly, the actor should refuse to take the prop if all procedures are not followed. If the actor themselves has broken the chain of custody ie by getting the gun off the prop table themselves or via an assistant then yes the fault lies with the actor.
3) Yes. This is where traditional gun safety applies, if the gun is kept pointed in a safe direction unless being directed to do otherwise then the only hole would be in the floor.
4) 100 percent yes
TL/DR: This situation is not as black and white as it may seem.