Prior to the introduction of model numbers in 1957, the M36 (or perhaps pre-M36 as it were) was known simply as the Chief's Special. If your gun does not have a model number stamped on the frame under the yoke, then it is not technically a model anything. The Chief's Special was introduced in 1950 and was the first of S&W's J-Frame revolvers. The new frame size was necessary because the frame window of the older I-Frame was too short to accomodate the length of the .38 Special cartridge. New-made S&W J-Frames, including the M36 "Classic" are actually slightly longer than older ones because the J-Frame was redesigned into the "Magnum" J-Frame in 1999 when S&W began chambering certain J-Frame models for the longer .357 Magnum cartridge (though the M36 specifically has never been offered in .357 Magnum).
In order to be a M36 or Chief's Special, certain features must be present beyond simply being a snub nose S&W .38. The gun must be chambered for .38 Special rather than the older .38 S&W cartridge, have a five shot cylinder, be a DA/SA revolver with an exposed traditional spur hammer, and have a carbon steel frame with either blue or nickel finish. Models which are commonly confused with the Chief's Special/M36 include the Terrier/M32, Regulation Police/M33, Chief's Special Airweight/M37, Stainless Chief's Special/M60, and the 2" barrel version of the Military & Police/M10.
Be aware that S&W does not officially rate J-Frames made before 1999 for +P ammunition. While an older all-steel J-Frame such as the M36, 40, 49, or 60 is unlikely to suffer ill effects with limited use of +P ammo (I shoot limited amounts in my own 1970's vintage M36), it's best not to feed them a steady diet of +P ammo. Under no circumstances should +P ammo be fired in an older J-Frame "Airweight" such as the M37, 38, or 42 because of their aluminum alloy frame which is likely to stretch if shot with +P ammo.
