With the introduction of USPSA PCC, I'm in the market to build a 9mm AR.

Do they use regular 5.56 AR free float rails?

I see there's a 9mm buffer, I'd it necessary over a carbine or H1?

Which is better, Colt SMG or Glock lowers? As far as reliability in feeding goes.

Can I use a standard stripped upper I have laying around?