Based on my experience on looking for a 9mm AR, I would recommend getting one that has a dedicated 9mm lower vs a universal adapted type. Also I went with one that uses the straight Colt/ Uzi sub-machine gun mags vs the Glock ones which look goofy to me and seem to have more feed problems in carbines. Be prepared to pony up $$$ for a good AR-9 they are not cheap! I have a Stag Arms dedicated lower AR-9 that has been flawless even w/ cheap dirty steel cased ammo. (It's not for sale.) Good luck!