The .357 SIG wasn't the first bottleneck handgun cartridge. In the 1960's Winchester necked the .357 Magnum down to to .257.Then the 9x25 Dillon came along in 1988 by necking the 10mm Auto down to .355". Finally in 1994, SIG Sauer and Federal with a joint venture, shorterned and necked down the 10mm to create the .357 SIG. Some think you can form it using .40 S&W brass, but the .40 is 0.009" shorter than the .357 SIG.
The idea of this cartridge was to try to match the 1450 feet per second 125 grain .357 Magnum, which is #1 in 1 shot stops in history. In a 4" barrel service pistol the Speer 125 grain Gold Dot .357 SIG is advertised at 1350 feet per second. Federal HST 125 grain 1360 feet per second. These two listed loads are two of the best we have to use in .357 SIG and I would feel confident with either, but Im a long Gold Dot fan. In chronograph comparisons I was able to find, you get 3%-4% more velocity when using a 4.5" Glock 31.
While it is not EXACTLY a .357 Mag, the .357 SIG has proven itself to be a very capable cartridge. Its very effective at barrier penetration (windshields,car doors, etc). Several Police Agencies have adopted it. The Virginia and North Carolina State Police, and even our local Sheriff's departments. As its popularity has risen with LEA's, its also became more popular as a personal defense caliber. Recoil is very comparable to a .40 S&W, just not as snappy. I'd take the .357 SIG over a .40 any time. Id also carry Underwood Ammo's 125 grain Gold Dot, thats advertised at 1475 fps and 604 ft/lbs, which gives you an amazing proven bullet at the original 357 Mag speed. They also offer a 147 grain XTP at 1250fps & 510 ft/lbs.
If you have not tried the .357 SIG, you really should. For us Glockaphiles, its as easy as a barrel from Lonewolf and your 22/23/27 can be a 31/32/33 no magazine change needed. Also the 10mm Glocks can be converted to .357 SIG with just a barrel, but the 10mm can also be a 9x25 which Im considering for my own G29 if I can find a bullet that can hold up to the speeds.