I called S&W and the guy I talked to there said that he never heard of this problem,(barrel nut coming loose on M&P 15 22)I ask any one who has this problem to call them (he also said I should not believe things written on forums) I also had to send a brand new 617 back because I did not notice the barrel was 1/16" over tightened until I went to sight it in,he also never heard of this problem.I guess I got the only two bad guns they made.I know any one can make a mistake but be good enough to admit it.I really like their guns I just did not like the guy I spoke to attitude.