The .357 SIG is an interesting auto pistol cartridge developed in 1994 by Federal Cartridge and SIG Arms. Like many other cartridges, it is misnamed, as it actually uses .355 inch (9mm) bullets. No doubt, the marketing mavens thought that linking the new cartridge's nomenclature to the famous .357 Magnum revolver cartridge would boost sales.

SIG's .357 is based on a necked-down and slightly lengthened .40 S&W case with zero body taper and a small 18-degree shoulder. The maximum case length is specified as 0.865" and the maximum cartridge overall length is 1.140". However, it headspaces on the case mouth, like a conventional straight case auto pistol cartridge, not on the shoulder of the case, like most bottleneck cartridges. This is important to note, because it turns out that reloaders cannot simply neck down .40 S&W cases to create .357 SIG cases--they turn out to be .01-.02 inch short. This messes up headspacing and adversely affects both accuracy and reliability. Use only actual .357 SIG brass for reloading.

Speaking of reliability, the feed reliability of the .357 SIG cartridge is very good, due to its rimless bottleneck configuration. The .355" bullet funnels easily into a chamber reamed to accept the 0.424" rim/body diameter of the cartridge.

The .357 SIG operates at a rather high maximum average pressure (MAP) for an auto pistol cartridge, having been standardized at 40,000 psi. This is higher than any other conventional auto pistol cartridge with which I am familiar. The 9x19 and .40 S&W operate at 35,000 psi MAP and even the big 10mm Auto operates at 37,500 psi MAP.

Factory loaded ammunition is available from Federal, Hornady, Remington, Speer, Winchester and others. The standard load is a 124-125 grain bullet (JHP or FMJ) at 1350 fps. This delivers 510 ft. lbs. of muzzle energy (ME) from a 4" pistol barrel (Federal figures). That puts it only 100 fps and 70 ft. lbs. behind the .357 Magnum as fired from a 4" revolver barrel. This is a flat shooting load for an auto pistol, with a midrange trajectory of just 3.1 inches with a 100 yard zero. Initially, Federal also offered a .357 SIG factory load with a 150 grain JHP bullet at a muzzle velocity of 1130 fps with 420 ft. lbs. of ME, but this load has been discontinued. Only 124-125 grain bullets are now offered by the major U.S. ammo manufacturers in .357 SIG factory loads.

A reloader with a .357 SIG pistol and a good supply of brass can do very well, indeed. The Speer Reloading Manual Number 13 shows that 13.1 grains of AA#9 powder can drive a 125 grain Gold Dot JHP bullet to a MV of 1287 fps. 14.6 grains of AA#9 can drive the same bullet to a MV of 1437 fps. These high performance loads used Speer cases, CCI 500 primers and were tested in a 4" pistol barrel.

The .357 SIG out performs all of the common 9mm cartridges, including the .38 Super, 9mm Luger +P and 9x21mm. Only the 9x23mm Winchester (124 grains at 1460 fps) has a ballistic advantage over the .357 SIG.

SIG, Glock, S&W and H&K (among others) chamber pistols for the .357 SIG. A number of police departments in the US have adopted the cartridge and they appear to be satisfied with their choice. It has proven to be a very good "stopper" with proper expanding bullets. For civilian shooters, the cartridge's biggest drawback is probably the relatively high price of factory loaded ammunition, compared to the more common 9mm Luger (9x19mm) and .40 S&W cartridges.

I am not entirely sure what motivated Federal and SIG to introduce the .357 SIG. It is an unusual cartridge because of its bottleneck case, afloat in a sea of more popular straight case cartridges like the 9x19, .40 S&W and .45 ACP. Yet, strictly on its own merits, the .357 SIG is a fine auto pistol cartridge, one of the most powerful and flat shooting cartridges available for service style autoloaders.