Slide Lock

I've got a minor issue with my M&P 9. The last couple of times I've been out to the range, the slide has failed to lock back after I fired the last round. I've got about 700 rounds through it and it's failed to lock back about a dozen times. A buddy of mine, who's been carrying an M&P 40 for over a year now had it happen twice while he was using my weapon. I've adjusted my grip since the first few times it's happened to make sure that my thumb wasn't riding the slide release, but it's still happening every now and then.



I was wondering if you fine folks might have some suggestions for how to remedy the situation. I'm running on the assumption that it's just stupid human error, and really hoping it's not something to do with my mags, but I don't know enough to really diagnose the problem.



Thanks guys![/quote]