N frames were originally designed (1905?) for .44 Special/Russian, and were also chambered in .45 Colt, .45 ACP, .455 Webley, and some others. Later on, they were also chambered in .38 Special and were the original vehicle for the .357 Magnum in the mid-30s.

K frames were originally chambered in .38 Special in 1899 and then in the 50s in .357 Magnum. The idea was to practice with .38s and then load with .357s for "business". That idea worked poorly in the real world. LEOs then started practicing with full power Magnum ammo and the revolvers started shooting loose and the forcing cone issue raised its head. That lead to the development of the L frames in the 80s, which paired the K frame's grip with a heavier frame and barrel.