my gas key screw wasn't staked good and backed out on a brand new m&p 15 after about 90 rounds not good . that's why i buy s&w so i don't have to worry about shipping it back . i own 3 m&ps but my new one failed in just a few min. i cleaned and checked everything when i got my new m&p home and everything was tight went out back run 2 mags through it took it apart to clean and the gas key had worked loose just got it home and have to work on it not good at all