I have a Bushy upper in 7.62x39 I bought last November that I use with my M&P 15 lower and haven't had any problems. Still, I keep hearing about feeding problems with many 7.62x39 caliber AR mags. Have you had any kind of feeding problems with yours?
BTW, I got 4 magazines in the mail during the past week for my gun, 2 from Bushmaster and 2 from ASC - who makes the "factory" 7.62x39 magazines for Bushmaster - at http://www.ammosc.com
. That's in addition to the 2 magazines that came with the upper. I ordered them separately back in January and finally
got them within a week of one other a few days ago. I don't know if they are just catching up on back orders or finally beginning to produce more mags but I like the mags and they seem to be the "gold standard" when it comes to mags for AR style rifles in 7.62x39. You may want to check them out.