I picked up a .40 S&W barrel for the P229 today. This is cool for two reasons. One, I can shoot the range's ammunition when I go practice, so $$$ savings, and I've got a lot of carry ammo and practice ammo of my own in this caliber. I also have the stuff to reload it. .357 Sig has a reputation as being a difficult round to reload, and if you don't do it right then the bullets can move back in the case as the ones above it are fired, resulting in a cartridge with higher pressures and a blown up gun and/or injury. I will not be reloading .357 Sig both out of concerns for safety and due to the extra steps it takes to do it correctly not being worth my time. I can make a lot more of the other calibers in the same time.
The sucky thing about the .357 Sig is a lot of the factory loads from the big name manufacturers are watered down. They do this as a cost savings measure. Instead of designing a projectile for .357, they just use their 124 gr 9mm projectile. These projectiles are designed to open up at a certain velocity. If you pushed them as fast as the .357 is capable of, they would open too soon or fragment, reducing penetration. So, they water them down so that they aren't much faster than 9mm +P ammo. There are specialty shops like Cor-bon and Buffalo Bore who load it like its supposed to be loaded, but then you get into the issue of training with one type of round but carrying something different.