Hatcher's Textbook of Pistols and Revolvers, pub 1935, is my go to manual on old pistol cartridges. 38 S&W = diameter of case = .383", diameter of cartridge head = .433"; 38 Special = diameter of case = .377", diameter of cartridge head = .433". I have loaded some 38 S&W for a friend after I got a die set in. I do recall the shell holder was same as 38 Special, but that was where the similarity ended.