Folks, the .357 SIG is nothing more than cleverly named 9mm* +P+ designed originally to make gun-unwise police administrators believe they were getting .357 Magnum in an auto pistol. At its best, the .357 SIG was about the same as the 125 grain .357 Magnum in a snub nose, such as the 2 1/2 inch Model 19.
The .357 SIG is not significantly different in performance than Winchester's 127 grain +P+ 9mm, but at way higher pressure, way higher cost, and way higher abuse on the weapons.
SIG's own entry in that caliber could not pass the Homeland Security trials and you will note that the only maker that passed those trials with the .357 SIG caliber was Heckler and Koch.
I have always been a big fan of the .45 ACP. As I am old, I have to guard against becoming "set in my ways." My opinions on the .357 SIG are the result of actual use. My study into the matter has also convinced me that the current crop of high performance 9mm loads, unlike those of years past, are not significantly inferior in performance from bigger calibers. When the only loads for 9mm were ball or hollow points that would not expand, it made sense to go to a bigger caliber. That is no longer the case, as projectile technology has come a long way. You get expansion and penetration and good performance on auto glass and all of the other barriers used in the FBI tests.
The Winchester RA9B and RA9T, which are one generation newer than the FBI contract 9mm ammo (Q4364) truly are good performers and well placed sources at Winchester indicate to me that the Bureau will switch to the 9mm, but that they will likely stay with the 147 grain weight as they remain convinced that deep penetration is the key to good stopping power. And with the 147 grain RA9B and RA9T, it looks like they are right. The other advantage is that neither RA9B nor RA9T are +P, they exhibit mild recoil and allow quick follow-up shots and are easy on the pistols. They also allow higher magazine capacity in a smaller space to fit smaller hands.
Adoption of the 9mm across the board by the FBI will also eliminate the annoying problem they have had out at Quantico with 9mm being dropped into a .40 caliber barrel and chambering a .40 behind it. A bang under these circumstances naturally results in a really exciting day at the range, as may be imagined.
The FBI faces the same difficulties that many other large agencies face in the recruitment and training of persons for the job. Unlike the gunfighters J. Edgar Hoover hired in the gangster era, they look for law, accounting and other technical areas of expertise, and a huge number of recruits have little, if any, prior knowledge or shooting experience. They are often not "gun people" in the same sense as many on this forum, and have little interest in firearms apart from learning to shoot what they are given in order to qualify.
The current 9mm ammo makes the 9mm pistol a viable choice again from a training standpoint, a financial standpoint and from other standpoints.
*For anyone who came in late, the diameter of the ".357" SIG is actually .355 (9mm), so it really should have been called the .355 SIG, but that would not have tricked anyone.