The M17 K-22 is more of a target revolver. It is just like the M16 Target Masterpiece in .32 Caliber and the M14 Target Masterpiece in .38 Spl.
The M18 Combat Masterpiece is the same revolver as the M15 Combat Masterpiece except for caliber. The M15 is a .38 Spl. and the M18 is a .22 LR. The M18 was initially designed as a training gun for Police Officers who carried the M15.
Jim