This is one you will have to make from a common cartridge currently available. It is close enough to .357 Magnum but the case will be a bit short, which really is no problem. .357 Maximum will give a full lrngth case if you insist. This link goes to a post about the cartridge on the Gun Boards web site (S&W 3rd Model Target / 38-44 Reloading | RVB Precision) It includes a dimensioned drawing of the cartridge and comments.