Most people have found that the 17rd mags (often really only 14-15rds) don't feed properly when you load them past 7 rounds. These are the ones that look like a 20rd 5.56 magazine.
AA actually specified a curved body 17rd mag, and the original C Products sent them a straight one that didn't function, so AA never carried them since they didn't work.
When I use them, I only load 5 rounds in them.
Also, my 10rd CProducts Defense mags hold only 9 rounds, but function 100% so far, over the past 2 years.
I have watched the 25rd mags run through Grendels for 3 days straight, with all-day shooting each day without any malfs.
For reliability with the PPC-based cartridges in the AR15, it helps to radius the edge of the ejector itself, and make sure your feed ramps are blended and polished.