I have a new M&P full size .40 that has never been fired, except once at the factory. The date is 3/28/06 and the serial # is MPBxxxx, so it is one of the first ones. I have heard that there were issues with the earlier guns, the current ones have upgrades, and that if I have problems, I can send it in and they will do upgrades. Were the # MPB's included in the problem guns, and do you know what the upgrades were?