I built an AR9 with a BCA bolt and barrel. I wanted to use regular Magpul 5.56 mags so I bought a Mean Arms pmag converter. I knew going into this I could possibly have trouble with feeding and cycling. I tested fired it yesterday, it had a lot of trouble. The mag would barely fit, I would have to press it very hard for it to seat. Every round that fired the mag would fall out, I noticed wear marks on the notch of the mag. I went home and dremeled that mag notch about a 1/16" and went back out later for another test fire. Now the bolt will not pickup a round from the mag, I must of taken too much off the notch in the mag. I am not very impressed with the Mean Arms mag converter, the feed ramps and ejector are made of plastic and took a beating with only about 10 rounds fired. I would say that after a few hundred rounds it would all be worn out the the point it wouldn't function anymore. I'm going to continue to work on this thing to get it running reliable but I would like to go a different route with magazine.
A few years ago I saw a similar mag converter to Mean Arms. It was like a block type device that fit in the mag, using it's current spring and follower. I just can't find anything like it, all that comes up when I search is the Mean Arms and the CMMG converters with are almost the same except the CMMG with only work with a proprietary CMMG upper. Does any body run this setup or one like it and if so what are you using?