They are only .356", and for .357 Sig, you should be looking for .358" caliber bullets.
I haven't tried that, but I would expect accuracy to suffer.
I don't know that I'd recommend this, but given the proper projectile weight and load, I'd suspect that you would get much better results loading .358" bullets in 9mm, if your cartridges passed the 'plunk test'.
Hmmm......everything I've read shows they use 9mm bullets.