You've shot it a lot?
Mine did that at first. I polished the inside of the chamber with a dry felt Dremel tip. I also sanded the inside of the mag lips with and emery board. I don't run it very dry though. I also keep the mag full because I keep it loaded all the time. I think that helps weaken the mag springs. I noticed that the slide closes much better without a full mag. I can pull the slide back an 1/8 inch and let go and it doesn't close when the mag is full. The upward pressure of the top round pushing on the bottom of the slide slows it down. My theory is that a dirty chamber+the pressure generated by the mag+the top round slowing down on the rough feed lips of the mag+weak recoil springs can cause the slide not to close.
Mine did that at first. I polished the inside of the chamber with a dry felt Dremel tip. I also sanded the inside of the mag lips with and emery board. I don't run it very dry though. I also keep the mag full because I keep it loaded all the time. I think that helps weaken the mag springs. I noticed that the slide closes much better without a full mag. I can pull the slide back an 1/8 inch and let go and it doesn't close when the mag is full. The upward pressure of the top round pushing on the bottom of the slide slows it down. My theory is that a dirty chamber+the pressure generated by the mag+the top round slowing down on the rough feed lips of the mag+weak recoil springs can cause the slide not to close.