I have had 2-Colt 7.62x39 Uppers,BUT I HAD 10 G-TECH MAGS,like the one in amphibians Blaster,if you can't find those mags,FORGET IT!!!!,As said by a number of AR Dudes,buy a AK for the AK rnd,and have fun making all types of differant uppers w/the AR..I am thinking of getting the .21 (5.45x39) Upper,the AR mags will hold the Rusian rnd,and from what I have read,they shoot Great,very accurate,and hit like a concrete block..I have a mint OLY preban Lower i bought from Stokes,and on top of it,I put a Colt style 9mm,so I have a fun Carbine in 9mm,it LOVES Wolf 9mm ammo,Wolf 9mm has guts,it is Hot,and w/the steel case extracts perfectly..If anyone sees this,and can answer why my Carbine with the same length barrel,out performs my UZI in 9mm,in Distance,and accuracy..The CAR15 w/9mm Upper out shoots the UZI bad,though the AR is ammo picky,where as the UZI shoots ANYTHING i put in it,from ammo that is 900fps,to ammo HP and 1450fps..At 130 to 150 yrds,the AR carbine is much more accurate,and puts a faster rnd down range??????