I think that the better way to say that is that the rifle was designed to handle steel case, foreign made ammo, but also to handle other fare. I have several 527s, none of which have any problem with brass cased domestic ammunition. In fact, all my hunting ammo is brass cased handloads, with standard primers. This in .223, 7.62 and 6.5 Grendel.
The problem most likely isn't the rifle. But, tolerances do vary. I had one 527 carbine that had chambering problems, I sold myself on thinking it was the ammo and today I think it was merely in need of a chamber polishing (it shot just fine, all ammo, just would hardly chamber a round). So, (shrug) best of luck to OP.
