 For the Model 36, they designed a small concealable, 5-shot, double-action revolver with a 2" barrel, that could fire the more powerful .38 Special cartridge.Since the older "Safety Hammerless" (I-frame) was not able to handle this load, a new frame was designed, which became the J-frame.The new design was introduced at the International Association of Chiefs of Police (IACP) convention in 1950, and was favorably received.