Hi Jerome! The 357 SIG is kind of its own thing. What constitutes .38 caliber encompasses about a dozen rounds with bullet diameters ranging from 380 ACP to 38-40 Win. The 357 SIG's bullet has a smaller diameter than all of those cartridges, and it's exclusively used in semi-auto weapons. The 357 SIG also has an unusual case design for a pistol cartridge in that it's bottlenecked – tapered, like a 223 rem or 7.62x39. I don't believe you could run 357 SIG through any .38 cal firearm.