Just realized the other day when I shot my p220, the slide didn't lock back after the last shot on neither of the 3 factory mags. I read about someone else having this same problem on another board. Someone suggested that I take all 3 fac mags and insert each (empty) in the gun (with empty chamber of course) and rack the slide back to see if it locks. I did this with all 3 mags and each one would lock every now and then. I also made sure my mag springs were inserted correctly in my magazines and also made sure my guide rod spring was inserted correctly. And topped it off with alittle more lubrication. I then made sure my grip was not affecting the slide release. I only have 50 rounds through this gun thus far but I think once I break it in with a couple hundred rounds, it may correct itself.