I remember an episode of the Better Call Saul podcast where Vince Gilligan was talking about safety on the set. This was WAY before this incident.
It was something about how they worked with guns and how they use squibs, etc. The way that actors are told about the guns they are using is that the armorer hands them the gun opened, fully emptied. The actor and the person being shot watches as the armorer handles the gun and it is in full view of everyone involved. The gun doesn’t leave the sight of the actor or the armorer as everyone gets in place.
Once everyone is ready, the gun is handed to the actor and then the scene is shot.
The amount of checking and double checking that is done is way over the top. And that’s just for a non-functioning gun For guns with squibs, even more oversight and more checking.
“We’re making a TV show for Christ sake. No one should get hurt, let alone die, because we’re shooting a scene.” (horrible paraphrase of Vince).
The actor shouldn’t “assume” the gun is safe when it’s handed to them. The actor KNOWS it’s safe because they saw it. The armor KNOWS it’s safe because it’s their job. There are no "should"s.