Older revolver catalogs used to list two basic butt shapes for their products—round and square.This actually meant slightly different things in the literature of the two big pre-World War II gunmakers—Colt and S&W.
For Colt users, round butts involved a light rounding of the lower corner of the revolver butt, front and back. Smith & Wesson's use of the term involved rounding the corners and slimming the back strap.
Further, the Springfield product enjoyed a slenderizing of the front strap, so much so that you needed a different length mainspring screw on the two different K-frame guns.
Just thought this might be interesting to a few.