I have a 2014 GCNM that is driving me crazy. When I first got it I would have a number of failures every mag, it went back to Colt twice. I'm still getting a failure about once every 50 rounds where the next round gets hung up on the feed ramp, leaving a dimple in the middle of the round. It locks the gun up pretty good. Have replaced the recoil spring on Colt's recommendation which did nothing. Any ideas?