I lied this morning. While riding around today, I recalled I had a failure to lock back at just under 500 rounds. Since I had not cleaned it, I decided to go ahead and clean it after that range session and troubleshoot the mag that gave me an issue on the previous session. After a couple of hundred rounds, I determined it was more than likely my thumb riding the slide stop. After giving up on reproducing the issue, I was getting a little tired and caught myself letting my thumb get onto it when gripping. Have not had the issue since. It has not been choosy with mags. It shoots the factory checkmates, other checkmates, other dw factory mags and wilson 47ds. At first the grippieness was a bit much, but I quickly got used to it and now love the feel. My other guns feel loosey goosey.