I have a Speer #3 and a Speer #7 reloading book and they spend a bit of time discussing the "balloon" or "folded head" AR case. I think it would be a bit of a challenge to find those cases still around, but one never knows. I would think any regular 45 ACP load would be fine in modern 45 AR brass in a modern gun. I think I'd stay away from anything close to ACP max in an older revolver using unknown AR brass.