One other thing, .357 sig is not .357 magnum. A magnum 125 gr bullet moving at 1650-1750 fps is something .40 S&W or .357 sig cannot touch. It is the real man stopper. If you want that kind of power in a semi-automatic, you need to move up to 10 mm.
There is one load I found from BB that meets those 357 Mag specs. The trade off is 1)
six shots vs 14-16 2)
Lots of blast,flash and recoil for a 150 FPS gain.
I do not think I would want to shoot those in my J frame.