The 357 SIG cartridge was released in 1994 for use in the SIG Sauer P229 pistol for use by the Federal Air Marshalls. It was essentially a 10mm case necked down to accept a 9mm bullet.
Initially, it was designed to use a .357” (9.02mm) diameter bullet, but this was changed to .355” (9mm) in order to accept of a wider variety of bullets commonly used for law enforcement, personal defense, and target shooting.
The intention was to better replicate the ballistics of the 357 Magnum 125-grain police load in a semiautomatic pistol. This was 1994, and 9mm ballistics had not quite improved to the level where they are today. A semi-auto pistol that could hold 10-15 rounds of ammo that duplicated the 357 Magnum load was more desirable than a 6-shot revolver.
Even though it was a necked down 10mm, the 357 SIG could fit into pistol frames designed for the 40 S&W by just changing out the barrel and recoil spring. 357 SIG rounds would fit in pistol magazines intended for 40 S&W, too.
357 SIG was intended as a law enforcement duty caliber and for lawful armed self-defense. Its bottle necked design makes it generally reliable from a feeding perspective, but it is not necessarily a favorite of hand loaders.
The round is most commonly found in semiautomatic pistols. While it would have made for a great mini carbine round, no major manufacturer ever offered a pistol caliber carbine in this cartridge. SIG teased an MPX carbine of this caliber over a decade ago, but nothing ever came to fruition.
Some outdoorsmen have used 357 SIG as a sidearm when hunting or fishing in bear country as a personal defense round. Anecdotally, one often hears of the occasional hunter using a pistol in 357 SIG against small to medium sized game, but it is not commonly used as a hunting round.
As it is a capable medium to large game round, it is sometimes used in self-defense when the user may not have had access to another type of firearm.
Perhaps the best known user of the 357 SIG has been the US Federal Air Marshall Program with the SIG Sauer P229, the first factory handgun chambered in this caliber. Other agencies to use 357 SIG are the Texas Department of Public Safety, Delaware State Police, Texas Rangers, Washoe County Sheriff’s Office in Nevada, the Virginia State Police and the City of Richmond, Virginia’s Police Department.
Because the round is inherently accurate and reliable, it has seen use as an informal target shooting pistol as well as with various action themed shooting sports. It never gained widespread acceptance among most mainstream shooters and is definitely more of a niche round these days.
357 SIG has a maximum length of about 33mm. Longer and wider than a typical 9mm parabellum and closer in size to a 40 S&W or 10mm.
Its recoil is best described as medium to stout depending on the handgun in which it is used. This has more to do with the material that the handgun is made from. In all metal handguns such as the SIG P229, SIG P226 or the 1911 it is controllable and on par with a 40 S&W. In polymer framed handguns such as the Glock, the recoil can best be described as stout, due to the lighter weight of the handgun.
Depending on the load in question, typical muzzle energy is anywhere from 500–700-foot pounds of energy.
SBR Ammunition offers 357 SIG in two varieties. One is XTREME DEFENSE with a 90-grain bullet. The progressive nose geometry allows for deep, straight penetration while creating a permanent wound cavity diameter exceeding that of most expanding bullets. To top it off, the bullet is solid copper or brass and is able to overcome barriers to penetration. It is environmentally friendly, target unfriendly, very unfriendly, downright obnoxiously unfriendly.
The magic happens with the nose design where the radial flutes force the hydraulic energy inward and then as the energy is restricted, it accelerates outward creating high pressure spikes damaging surrounding tissue.
Another load offered by SBR is a 125-grain bonded jacketed hollow point (JHP) using a Sierra Sports Master bullet. This is as close as a shooter can get to firing a 357 Magnum load through a standard sized semiauto pistol.