It was loaded with dummy rounds, and one real round.
Can you tell the difference with a glance? No? And you expect actors to be able to tell?
He wasn't just fucking around with the gun, either, he was working with the director and cinematographer for a camera test.
The three of them were walking through the motions that would be used for the actual scene, complete with costumes and props. They were trying to get the positioning and lighting right.
I don't know why this is so hard to understand for you.
And again, he doesn't need to go through any process, because the precedent here is clear. The armorer is the person with the full responsibility for making sure that the weapons on set are safe. She was the one who loaded the gun.
If this happened in any other state, Baldwin would never have been charged. But it's New Mexico, and Baldwin made fun of Trump. The prosecutor is trying to make a name for himself by going after someone Trump hates.