I could be wrong, but that seems to be the consensus. Even on SIG's website. Course, the internet has failed me before. I'll double check.
Now, getting a .357 SIG barrel is another matter. I suppose my gun shop can get one without problem.
Keep in mind, those that are brand spanking new to firearms, that the .357 SIG round is NOTHING like the .357 magnum round. Both are very powerful effective rounds at the receiving end, but the SIG variety goes in semi-auto pistols, and the magnum goes in revolvers.
Price is a big difference. Plain Jane retail .40 costs $20, .357 Magnum is $25, and .357 SIG is $30. Generally and comparatively. Your mileage may vary.
Say you conceal-carry a P229, and you have both barrel options and plenty of practice with each... Which caliber do you carry with you for emergencies? I don't know, I'd need to do a lot more research and I am not pressed for time in non-carry civil-rights-quashing state of Maryland. While the .357 SIG looks screaming on paper, it might be too much. Chime in if you have any experience with it.
If you look at just the numbers published by ammo manufacturers, and compile them by muzzle energy you get a table where .357 Magnum is generally near the very top, with .45+P and .357 SIG intermingling close up there in the same area of the top of the table. All over a swath of .40 caliber on the table, then the rest... 9mm and .38 and .380 at the bottom.
Rule of thumb for regular ammo; .357 mag is around 550 foot pounds, .45 is 400, .357 SIG is 475, 9mm is 350, and .40 is 425.
The lowly 'minimum' self defense round .380 is around 200 for the hotter stuff.
Energy is mass (in grains) times velocity (in feet per second) times velocity, all divided by 2 times 32.1739 times 7000.
Muzzle energy is NOT the be-all end-all measurement of cartridge efficacy, keep in mind. Colonel Cooper would rise up from the grave and hunt me down with a pistol shooting 230 grain full metal jacket .45 ACP if I maintained energy was the only measure.
My mind right now, while the .357 SIG is impressive, it's not THAT much more impressive.Another future purchase/accessories idea is the .22 conversion kit for same. That's one gun that shoots 3 calibers with a quick takedown and swap out. Cool! Of course the conversion is pricey at $370. 1911 conversion kits run in the low $200s.