[Unclenick]

It's the design of the case. Been that way since the 1980's at least, which is when I first focused on .45 AUTO. I was using Lyman dies at the time and found Remington cases had the thinnest and hardest brass at the case mouth. After a couple of reloads it got so springy it was no longer sizing down enough to hold a bullet. At that point I stopped even picking Remington brass up at the range. Left it all for someone else to "enjoy" fussing with.

That said, if the carbide sizing ring in your sizing die was a little smaller, it would still make them work. I have not noticed Remington cases that sneak past me failing to work after sizing in Dillon dies, which tend to be a little snug. I don't know what the new Redding two-ring carbide dies would do with it either. You could call either one and ask, if you really want to use them. I'm concerned the mouths will split earlier than other brands because of the hardening issue.

I mainly use Starline bulk brass I buy new these days.