It is OK if they can’t recognize a dummy round. All they need to know is there is a round in the chamber, and then go get the armorer and ask why that is and if it is explicitly OK. Wat you don’t do is just assume it is OK. Everybody on set should have been required to have basic firearms training as a condition of working around guns. Every single person.
I already said there should not have been any live ammo on the set.
The armorer’s job is to streamline things so that the actors and director can focus on the task at hand. Anyone holding things up for questions is gonna get dragged.