The ism cartridges are not based off the 404 Jeffries like the Remingtons were. Slightly smaller in diameter.
Hmmmmmmmm !
Winchester Short Magnum, or WSM, refers to a family of rebated rim bottlenecked centerfire short magnum cartridges developed in the early 2000s by the U.S. Repeating Arms Company, the maker of Winchester rifles and one of the oldest firearms manufacturers in the United States. All of the WSM cartridges are based on the .404 Jeffery non-belted magnum cartridge which is shortened to fit a short rifle action (such as a .308 Winchester). RJ