-Or, has anyone tried to make a USGI mag work in a 7.62 upper?  

MG

If you can do a search here (if you can't here's a plug to get a membership so you can) you'll find a lot of opinions on this.  Most say the USGI twenty rounders work great.  I used to own a pre-ban 6830.  When I compared the factory "small-cap" mag to a standard USGI twenty I swear there was some minor difference in the feed lips or follower.  I wish I had pictures to be more accurate.  But at any rate I had patchy success with USGI twenty's feeding.  I also tried loading USGI 30's with about 7-8 rounds, IIRC and they seemed to work as good as the twenty's- which neither was really good.  It seemed to me the rounds in both mags kept trying to be stripped from the mag straight in line with the barrel and submarining causing a FTF.  I sold it and included some newly purchased USA frankenmags which people say are the best hi-caps for the 7.62 AR's.  I have not heard from the purchaser and that was years ago, but before it was out of my hands I dry cycled rounds through the mags and they seemed a lot smoother with the 7.62 round than the USGI.  Of course, doing it by hand is not quite the same as in the rifle, but the USA frankenmags certainly seemed to hold the geometry of the round better.  Wish I had bought more of those frankenmags at the time to sell later as sellers are pretty "proud" of them today!

GoGo

Edited for grammer, or lack thereof.