So I used these mounts for several guns that take GLOCK mags -- to include a GLOCK-17 and two AR-9s. The mount is find for the GLOCK-17 and one of the AR-9s, but the 2nd one the gun kinda of wobbles on it doesn't sit level. I believe the issue is the gun that doesn't sit level isn't well balanced (shorter barrel) and so more weight is in the rear of the gun. There is a little play between the mount and the mag-well on the gun. Since the other two guns are more evenly balanced it is not an issue, however, on the gun that isnt' well balanced it's an issue. I'd like to see these mounts fit more snuggle in the mag-wells.