Hey, Rastus,
Did you ever decide what kind of PCC you were gonna build? I did a blowback 9mm a few years ago. I used a CMMG lower that was set up for Colt-type 9mm stick mags. I've been happy with it. It runs well and doesn't beat me up that much, even with the narrow Blade brace. I can provide a parts list if you're interested. If I built another, I would NOT use the stupid gas deflector ejection port cover. It was a PITA to install, and I don't think it does that much. I do like the SMG-type mags. IMHO, they're more reliable than the vaunted Glock mags.
All my best...