+1. Why people get off by spreading misinformation has always mystified me, but it happens whenever someone asks the question about the 7.62 x 39 in an AR. I have two uppers, a 20" Colt I've had for almost 15 years, and another I built with a 16" Shaw barrel several years ago. Both work great. The Colt has standard feed ramps, while the 16" has extended cuts. I can't remember the last time I had a failure to feed with either one of them. No broken bolts. I bought a couple of extras years ago because of all the bad press, but haven't needed them. I started out using 20 and 30 round frankenmags (they worked) at the beginning when I got the Colt upper, and later on bought CProducts 30 round mags when they came out. Those mags were very hit or miss when they came out, but they fixed them. I also have a couple of the AR Stoner marked mags from Midway and a couple ASC mags. They work. The 10 round mags work as well, and I use those as much as I do the 30s since they are more compact. I see ASC has a 20 round mag out now, but I haven't tried it. I have gotten 3 or 4 mags I have had to return, but the ones that work just work.

The 7.62 x 39 is a great cartridge. I have been shooting cast bullets from the 16" as well. I won't say what kind of groups I am getting because no one would believe me (except for those who are already hip.)