Few experienced handgunners question the legitimacy of the .357 Magnum caliber. While it still has the limitations of any handgun cartridge, it has developed a reputation as a fight-stopper since its introduction in a revolver by Smith & Wesson way back in 1935.

The .357 Sig is a cartridge that was designed to allow for near-.357 Magnum ballistics in a semiautomatic pistol. And there’s a lot to know—and like—about the .357 Sig. Here are some of the most interesting facts about this unique cartridge.

  1. It’s a .357 Mag for Pistols Projects like cartridge development are always a team effort. In this case, SIG Sauer worked with Federal Premium Ammunition to develop the cartridge for release in 1994. The goal was to provide similar magazine capacity and dimensions of the popular .40 S&W, while replicating the ballistics of the revolver-only .357 Magnum.

Light bullets, like these Barnes 80-grain TAC-XPDs, loaded by Doubletap Ammunition, reach velocities over 1,700 feet per second from a pistol.

And it’s nearly the same. The “classic” loading of a .357 Magnum cartridge has a 125-grain, .357-inch diameter bullet launching at about 1,500 feet per second, give or take, depending on the specific load. The .357 Sig can do almost that, with most factory loads launching a .355-inch, 125-grain bullet between 1,350 and 1,450 feet per second. However, the .357 Magnum can also launch a much heavier bullet, like a 158-grain one, at high velocity. Due to case length limitations, .357 Sig loads only get up to about 150-grains at the high end. But you get the advantages of easier carrying and concealing, improved handing by those with smaller hands, and more ammo capacity with a pistol chambered for the Sig round.

It’s Reliable While the lower diameter and case rim dimensions are exactly the same between the .40 S&W and .357 Sig, the Sig round has a bottleneck profile to hold the smaller .355-inch diameter bullet. The case itself is also 0.009 inches longer. The bottleneck-shaped cartridges feed smoothly from magazines into the chamber, so .357 Sig guns have proven themselves to be extremely reliable. (Some folks make their own .357 Sig cartridge cases by reshaping .40 S&W brass. That will work, but isn’t recommended because the cartridge will end up being slightly shorter than its official specification.)

Clockwise from top right: SIG Sauer P226, SIG P229, and the new SIG P320, all chambered in .357 Sig.

Highway Cops Like It A surprising number of state highway patrol agencies have adopted the .357 Sig caliber. If I had to guess as to the popularity in that specific community, I would surmise that highway patrol officers might be more likely to engage in road incidents requiring car door penetration. The extra velocity of the .357 Sig gives it better penetration performance over slower rounds such as the 9mm and .40 S&W.

Other notable law-enforcement organizations have used the .357 Sig over the years, including the U.S. Secret Service, Federal Air Marshals, and the Texas Rangers.

Not all Loads are Equal Some manufacturers choose not to provide the full performance capability of the cartridge. For example, Hornady loads its .357 Sig Critical Defense ammo with a lighter 115-grain bullet traveling at only 1,235 feet per second. Their 135-grain Critical Duty load moves at 1,225 fps. On the other hand, Mike McNett, the godfather of Doubletap Ammunition, loads his 125-grain cartridges to cook along at 1,525 feet per second. If you want to be all you can be when using a .357 Sig pistol, choose your ammunition carefully.

Most pistols chambered in .40 S&W and .357 Sig. can use the same magazines.

  1. The P229 Was Tweaked for It As you might have guessed, the first handgun released for the cartridge came from the inventors. In 1994, SIG Sauer released a specially designed version of the popular P229 pistol to handle the higher pressures of the .357 Sig cartridge. Just in case you were wondering, the maximum pressures are either 40,000 pounds per square inch or 44,240 psi depending on whether you get your figures from Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI) or Commission Internationale Permanente pour l’Epreuve des Armes à Feu Portatives (C.I.P.).
  2. It’s Powerful Kinetic energy is one measurement of the “oomph” of any given cartridge. While you can’t make generalizations that one bullet is twice as good as another if the kinetic energy is doubled, you can use the measure as a guideline. Many other factors like momentum, diameter, and bullet design come into play if you’re trying to develop a picture of the overall destructive power of any given caliber and cartridge combination.

In addition to being necked down, .357 Sig cartridge cases (right) are just a hair longer than .40 S&W cases.

With that said, here’s how the .357 Sig stacks up against some other common cartridges. .357 Sig with 125-grain bullet at 1,450 fps: 583.7 foot-pounds .40 S&W with 180-grain bullet at 1,050 fps: 440.7 ft-lbs .45 ACP with 230-grain bullet at 850 fps: 369 ft-lbs 9mm with 115-grain bullet at 1,150 fps: 337.8 ft-lbs .380 ACP with 90-grain bullet at 950 fps: 180.4 ft-lbs

These Speer Gold Dot bullets demonstrated perfect expansion performance. The extra velocity helps improve performance consistency.

If you want one of your own, SIG Sauer makes a variety of handgun configurations, as does Glock and Springfield Armory. If you look on the used market, you’ll find them from other manufacturers as well. For example, Smith & Wesson chambered its M&P full-size and compact models in the caliber.

The author fired these Hornady Critical Defense .357 Sig bullets through floor tile and they still expanded perfectly in the gelatin block behind.


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