In 1959 the folks at Olin/Winchester decided to offer a rimfire cartridge with some extra zing over the quintessential .22 LR cartridge that dominated-and still does-the rimfire market. As has often been the case, the gun-manufacturing side of Winchester lagged behind the cartridge-development side, and it took another year before the Model 61 would be available in the new cartridge christened the .22 WMR or Winchester Magnum Rimfire.
The Model 17 K-22 Masterpiece .22 LR revolver was Smith & Wesson's finest double action (DA) rimfire revolver and, along with the Colt Diamondback .22, probably the best rimfire target revolver available anywhere. A version of the K-22 Masterpiece revolver is still offered today, as the Model 17 Classic.
That makes sense. I've always wondered about having a second cylinder in one of these for .22LR and if S&W didn't encounter the same issues that Ruger did with their convertibles...