This is a K38 Combat Masterpiece from 1953. Square butt, 4" barrel, s/n K 194xxx. There is no model number stamp, just assembly numbers on the frame and the yoke. The s/n is also on the cylinder and the barrel. It needs a good cleaning and has been in a leather holster for a very long time. The cylinder is extremely difficult to move open like the yoke is just gummed up. While the trigger is very smooth, the reset is weird. It's like there are 2 reset points, if I just go to the first, it's locked up, but then if I release the trigger all the way, it resets and it is fine.
My wife brought it home from work, at the church. The revolver belongs to a family friend who also runs the food pantry associated with the church and he knows I like S&W revolvers (60 from 1979, 6" 28-2 from 1982 and 66-8 from 2015). I offered him $400 for it and he doesn't want to sell but wants me to hold on to it for him. Regardless of him selling it, I offered to disassemble and clean it for him. I'm hoping the cleaning will take care of the stiffness in the yoke when the cylinder is opened and improve the trigger reset.
They started in 1899 as the K frame M&P 38 (Military & Police) but in 1947 evolved to the K38 Target Masterpiece which were standard with 6" tapered barrels. The FBI wanted a 4" version with a heavy barrel and Braughman front sight like this one and they started in 1949. In 1957 it was renamed the Model 15 and stayed in production as the 15-8 until 1999. The "dash" numbers designate engineering changes. The 15-9 was a limited production run in 2002 and the 15-10 was re-released 2011 under the classics line and is still in production. The Model 67 is the stainless version introduced in 1972 and is still in production.