Thanks! Prying it a bit plus a little squirt of Rem Oil and it slipped on with a some light persuasion, lol.
I've got some aluminum GI mags that I've got to dig out so I haven't tried them yet, but the steel ones that came with the gun fit pretty good, maybe a bit loose but nothing that's affected function yet. Is there anything I can do about the PMAGS? I don't much like the idea of having to sand or otherwise modify a brand new product for it to work, but if that's whats gotta be done…