People think "prop" means fake. Nobody ever mentions the 'prop' microwave in the kitchen on a tv show. Or the 'prop' pen, or couch. Those are all props and they are all usually real, functioning items. There are special people who are responsible for those items; they're called property masters. The ones who handle firearms are usually different from the ones who handle everything else due to the inherent dangers of having an actual firearm on a set with so many people who might have access. These people fiercely guard and control these firearms because they are NOT fake. Their careers are on the line if an accident happens or even if a chain of custody is broken.
I'm curious to see what the deal is when they announce the type of projectile that killed the unfortunate lady. Perhaps actual real rounds were being used some reason - if so, then the entire blame lies on the person pulling the trigger as they would have 100% known fully well that they were holding a charged firearm. Okay, perhaps some blame might go to the property master or trainer or handler for not stressing the common proper safety protocol of keeping the finger off the trigger, if it can be proven that they failed in that regard. So many variables that we don't have answers to right now.
I just hope that this situation doesn't turn into a campaign to aid the anti-gun crowd. My belief is that movies are make believe so that means that the actors in them are literally playing with guns when using them in the production of a movie. And what's rule number 1?...never play with a gun.