I have CProducts mags in 5.56, 6.5 Grendel, and 7.62x39. The 5.56 mags are both aluminum and stainless steel, in 20 and 30 round capacities. My observation has been that the aluminum magazines have been fine, but the steel ones are the ones you are going to find out of spec. That isn't to say all of them are. All the ones I have now are great, and work as well as any magazine out there, but I had to send a few back for exchange back when I bought them a few years ago. I like their stainless steel mags, especially the older ones with the Marlube finish. If the mags with the rifle you are looking at have all been proved out, you will be OK. The quality of the mags depend somewhat on when they were made. Whenever CProducts came out with something new, there was usually a period of time before they got things sorted out.