[Cobra64]

You may be confused as to the difference between a .357 magnum, typically shot in a revolver, versus the relatively new round .357 Sig that was developed in 1994. The new cartridge was named "357" to highlight its purpose: to duplicate the performance of 125-grain .357 Magnum loads fired from 4-inch barreled revolvers, in a cartridge designed to be used in a semi-automatic pistol.

The .357 SIG provided a self-defense cartridge close in performance to a 125 gr .357 Magnum, but from a semi-automatic pistol with greater ammunition capacity..

.

.

Both my Sig Sauer P229ST and P226ST can be chambered for all three calibers shown above.

.

[Wonder Warthog]

"You may be confused as to the difference between a .357 magnum, typically shot in a revolver, versus the relatively new round .357 Sig that was developed in 1994. The new cartridge was named "357" to highlight its purpose: to duplicate the performance of 125-grain .357 Magnum loads fired from 4-inch barreled revolvers, in a cartridge designed to be used in a semi-automatic pistol."

That is precisely the case (and part of the reason for my qualifier question in the original post). Squantos and others (you included) have been excellent sources of info. I have seen an article in the NRA mag (American Rifleman) on the cartridge fairly recently (I think late last year), but didn't garner the details given in the responses here from that article. I'm pretty sure there is at least one "true" .357 magnum semi-auto, but I gathered that it was "unusual" and a rarity.

Again, thanks to all who responded.