Others will have MUCH more knowledge on this than I... my sentiment is that whatever AR 9mm upper you buy... you probably have to purchase mags that are compatible. It's not a one size fits all. The prices on 9mm uppers are in the $500-800 range, which is TWICE the price of a basic HP carbine in 9mm. That's a lot of cash.

I'm looking for a 9mm carbine upper because I want to remain true to the manual of arms for an AR. Not because I distrust the HP Carbine.

Dafadda

Yep! ^^^^^^^^^^^^^^ What he said.:)