I have a m&p 40c serial number MPNxxxx. My pistol developed the mag drop problem. I purchased my 40 from Gander Mountain and their gumsmith sent it to Smith&Wesson, 1 week later my 40 was back with a new mag latch. I put 3 mags thru it and the mag dropped again!! This time I called S&W myself, they sent me a shipping label and away it went. 8 days later my 40 was back with a new and improved mag latch. I took it to the range and mag dropped again! A friend of mine bought a 40c just like mine and one day we were shooting at his backyard range. We were talking about my problem and how his 40c did not have ANY problems. We decided to try to resolve this mystery. We use the same ammo, the same model 40c but the only difference was the mags. I marked my mags with a silver 1,2,3-- I have 3 mags. we swapped mags and the mag drop followed my mag number2. I shot his mags perfectly. Mag 2 is an orginal with the 40c when I purchased it. Since then I have put 500+ rounds thru my 40c and NO problems what so ever!!! So the moral of this story is check your mags. Smith&Wesson customer service is OUTSTANDING. I called them back and let them know what I found. I am currently saving up to buy a M&P9c. I hope this helps someone else with this problem.I would recommend a M&P to anyone.