Just to clarify ammunition terminology, the .38 S&W cartridge goes back well into the 19th Century, and is one of the earliest American center fire metallic cartridges of the black powder era. It has a slightly larger case diameter than the later .38 S&W Special cartridge, which also has a longer case. The two are generally not interchangeable in the same chamber. The early .38 S&W cartridge in the USA was usually loaded with a 146 grain lead bullet. After WWI, the British decided to replace their .455 military revolvers with something smaller. So what the British did was to take the American .38 S&W cartridge and substitute a 200 grain lead bullet for the old American 146 grain lead bullet. And they then renamed the cartridge as the “.380 Revolver, Mark I.” It was NEVER officially called the .38/200 by them. Later on, the laws of war were rewritten and codified under the so-called Hague Convention. Thereafter, the use of expanding lead bullets in warfare was verboten, as being “too cruel.” To comply with The Hague Convention, the 200 grain bullet was then replaced by a 178 grain FMJ bullet, and, in time for WWII, the cartridge was renamed by the British as the “.380 Revolver, Mark II.”. The Official Commonwealth military nomenclature for the S&W M&P revolver of WWII was actually the “Pistol, Revolver, Smith and Wesson, No. 2,” No. 2 meaning .38 caliber. Not sure what the Tommies called it unofficially. Could have been .38/200, could have been K-200, maybe even others. Probably not the Victory Model, which was also unofficial.