S&W Combat Masterpiece
Sorry, I don't have my copy of the Supica & Nahas book, Standard Catalog of Smith & Wesson at hand, so I can't give specific dates.
There are two ways of looking at this fine revolver - - First, that it was an upgrade or modernization of the Hand Ejector target model - -ie: a Military & Police with adjustable sights. This was on the basic 1905 Hand Ejector frame, later called the K frame, lighter in weight than the then-popular Outdoorsman model, which was built on the N frame, or .44 and .45 frame.
The other viewpoint is that S&W was building a series of fine target revolvers on the K-frame - - K22, K32, and K38, in those respective calibers, practically all with six-inch barrels. The K38, besides being an excellent target revolver, was popular with police officers - - Lighter than the N frame guns, and, besides, many departments didn't allow their cops to carry the .357 magnum cartridges, so there wasn't much use in lugging the extra weight around.
The six-inch barrel made for rather uncomfortable carry in a patrol car, and four inch revolvers were already very popular. S&W responded to market demand for a fine, target-sighted, DA duty revolver in medium weight. They shortened the K38 barrel to four inches, narrowed the rib atop the barrel to further reduce weight, and, LO! the Combat Masterpiece was born. Along with the target rear sight, a trigger stop was fitted, at least into the early 1970s.
All this took place sometime around the early 1950s, as I recall. For some reason, S&W didn't see fit to offer the two inch model 15 (as it was later designated) with the round butt.
The Combat Masterpiece was, of course, the direct ancestor of the Model 19 Combat Magnum - - Essentially the same revolver with a longer cylinder for the .357 cartridge, and an underbarrel lug added to tame the magnum's recoil a bit.
Hopefully, someone else can provide exact dates for some of these changes . . .
Best,
Johnny