i had a sig 229 in 40 S&W with a spare 357 sig barrel... it is my understanding that the 357 sig was developed to mimic 357 mag ballistics and that one of the benefits is the ability to penetrate auto glass without stripping it's jacket. FWIW i have no idea, never shot auto glass to see.. but i've read a lot of the development articles on the round... one problem that was and is encountered is setback of the bullet in the magazine under recoil do to the short neck which limits the clamping area on the bullet... it needs a very firm taper crimp to hold the bullet in place...