Just curious, what guns/mags in your experience have given you issues in this way? I've had AR mags not want to seat fully when loaded to full 30, a sharp tap and tug usually corrects that, but curious about your experienceI think it's important the "burn-in" period is done with mags loaded to full numerical capacity. That is where I have seen most problems; either the mag won't seat under a closed slide at full capacity, or if it seats, the gun won't strip the top round. This is what I love about my Sigs; if something is advertised as 21-round capacity, you can load it to that level and it will work under all circumstances. Not all are like that; some have to be down-loaded. Only by loading them to full capacity and using them extensively, will you know.