Here's a set on my 4506-1 and the gap is not really that discernible unless you know there's not supposed to be one. The xenoly grips are made tight and the open end has to be pulled apart slightly to get them into the frame, that helps to minimize the size of the gap (mine is between 1/32" and 1/16"... 3/64"??) when the grip springs back into shape.

I find the benefits far outweigh the minor cosmetic "flaw", IMHO I think they are what should have been put on the big 3rd Gen pistols to begin.

I bought these and a set of curved back grips directly from S&W about 6 months ago.