Mike - Your Model 13 with the 3" barrel has the round butt. Yes it is a "K" frame, but usually the shorter barrel versions i.e. 2" & 3" have the round butt and the longer barrel versions i.e. 4", 5", 6" etc have the square butt. Here is a pic of my two S&W Model 10 service revolvers [kept them after we converted to the Glock .40 cal pistol].
The top is a 4" Model 10 "K" frame .38 Special with the square butt and the bottom is a 2" Model 10 "K" frame .38 Special with the round butt. Note the profile of the round butt "K" frame is identical to your Model 13, 3" in .357 Magnum...[Further note: S&W also did some of the longer barreled "K" frames with round butts, and vise versa, too]...

[Sorry for the pic quality, both revolvers have been welded up and mounted in a box frame as a momento, so the pic was taken thru glass...]
BTW - the Pachmayrs for the square butt will fit the round butt model, but for carry I'd recommend the round butt style like I have on my S&W "J" frame Chief's Airweight in .38 Special...[same style but one frame size smaller]. Specify to your dealer that you are looking for "K" frame grips for a round butt...


Regards, Marcus.

Edited by North Logan