The PM was Sarah Zachary, I think? She was given immunity and has a vested interest in maintaining that immunity.
Just like as with the whole ...plinking in the down-time... rumors, this whole thing about using live ammo to make dummies is pure supposition; there are no media reports or speculation of it and, as far as I know, not a single person has ever said that they heard HGR talk about doing it, let alone actually see her do it. There simply is no evidence for it. Once again, if there were evidence that that was her intention it would surely have been brought up in evidence as that would go a long way towards explaining the origin of the live ammo because if they can demonstrate that she intended to do that then they've basically proved that she provided the live ammo or at least knew it was there.
I had to go back and look up some info to make sure but it was a production manager named Katherine Row Walters, not the prop master that HRG was working with, that locked the trailer with a new lock after the shooting and later let HRG have access to remove items. And the inertia puller was bought by HRG and she billed the movie company for it.
And Marantz4250b is right. There's easier ways to make dummy rounds if you have the proper tool. I didn't deal with soft lead when I made mine. But that doesn't mean that HRG knew that.
The inertia puller is interesting, and I have my opinions on why she bought it, but I don't think it really affected the case. Not when they have HGR on video saying that she didn't know where the box of rounds came from, and she didn't check them before loading the gun.