Hello
I Believe you are speaking of a Model 30 or 31 Here. They are I frame revolver's or Later ones were-J-frames. The K-31 was never made by S&W. They did now ever make a K-32 that was a much larger K-frame in .32 S&W Long Caliber with a 6" Barrel and adjustable target sights. Two very different revolvers here. The Model 30 & 31 are more common and cheaper to purchase. They most times had a 4" barrel and were fixed sight revolvers. Regards, Hammerdown