Some ARs seat fully loaded mags easy and some don't. Nothing to worry about. AR Pmags are good to go. So are the 20 and 25 rnd AR 10 mags. Most of my mags are USGI aluminum but I have about 50 Gen 2 Pmags as well. I have only had one Pmag that didn't work and that was a used and abused Gen 2 i found off roading. Figured out why it was let there real quick. I filled it with JB Weld, painted it yellow and use it for a vice block when working on ARs.