The .357 Sig is supposed to match the ballistics of the .357 Magnum, but in a rimless auto cartridge. Unfortunately, it does not achieve this. With 125 grain bullets, it comes close, but with heavier bullets it cannot match the .357 Magnum. Shortly after it was introduced, it was embraced enthusiastically by many police forces, but popularity now seems to be declining, and the cartridge may become somewhat of a passing fad.
I have a .357 Sig barrel for my Glock 22, and it is fun to shoot sometimes. The recoil is roughly equivalent to a .40 S&W, perhaps a little lighter but definitely sharper than the .40 S&W.
I was shooting some handloads made with Blue Dot, and an unburned flake of powder ended up in the chamber. It got lodged against the shoulder of the next cartridge, the action wouldn't close, and it wouldn't fire. Cycling the round did not clear it. Because of this incident, I will think twice before choosing to carry a bottleneck autoloader for self-defense.