Yes you need different mags for 7.62x39: http://www.primaryarms.com/asc-7-62x39mm-30-round-ar-15-magazine-mgasc762-30rd-ss
Damn it... Ok, so we are back to .300 BO...
I guess that's fine, let's me use the shorter barrel, packs more punch than .223 and if I decide to suppress it, its the better caliber for that...
@IntegrityArms , do you guys have the barrel, upper and quad rail and things in stock to build a nice, but not crazy expensive 8.5" upper, in stock? If so, I am only 30 min away and can head over this afternoon or tomorrow.