I just purchased an MPX 9 mm last week...cleaned it up and shot it on Sunday. I had a bunch of failure to feeds when the 30 rd mag was filled beyond 5 rounds (bolt was not completed settling the bullet into the chamber). I brought it home to do a complete tear down. I tried to remove the barrel, and same thing happened. The exact same nut for that barrel screw stripped out the upper. Called customer service, and now I got to drive the thing back to the Pro-shop to be delivered back to the factory for repair. Luckily, I don't have to mail it cause I purchased it from their pro shop, and I live within and hour of the Pro Shop here in NH. Sucks, because I really want this gun to work, and have been previously happy with the two sig's I own (one I carry on duty). All I can say is if you want this gun, I would wait till they get all the bugs out of it. Here we are, over two months after a known problem, and I don't see anything different from my gun than from the previous poster. You would think they would have taken the 5 minutes to make sure this wouldn't happen to somebody else before I walked out of their main store. If I knew about this problem, I would have had their armorer at the shop do a complete tear down in front of me before picking it up. They have treated me well in the past, but they should be picking up the bill for shipping it back to the factory. In the meantime, I have $1600 invested in something that doesn't work.