Believe they are L-Frame grips and I know that sounds odd but there is a reason for it.
While the grip frame is smaller than the N-Frame, it allows a larger amount of rubber in the X-Frame grips. More rubber = more recoil absorption which is a very good thing in the X-frames!
The X-frame grips also fit N-Frame round butt guns well. Unfortunately you can only get them from S&W Directly.