I have one of the new Ruger RR that take the AR 15 mag. Its a nice little design, that took a lot of machine work on the bolt to make it work, but it does work fine. The heavier bullets have to be seated a little deeper than I like due to the Pmag included. But that being said, after a few rounds have been ran through the gun it seems to function a little smoother. Great set up though, especially for those of us who have several ARs.