I took my AR-15 up camping recently and had a really hard time getting the PMAGs to lock in. I had to ram them home pretty good to get them to lock. Not problems once I got them in though and my CMMG .22 conversion kit mags worked just fine. The gun and the mags sat in my pretty warm car for a day and a half before I brought it out, and that is the only thing I can attain it to. I tried half loading them, ripped off my recently applied mag wraps :-x , etc. Got home, tried to replicate and had no problems at all.