Glock 31

What Is .357 SIG and Why Was It Developed?

The .357 SIG cartridge was developed jointly by SIG Sauer and Federal Cartridge in 1994 to replicate .357 Magnum ballistics in a semi-automatic pistol. It uses a .40 S&W case necked down to accept a 9mm (.355″) bullet, producing a bottleneck cartridge that headspaces on the case shoulder and runs at high pressure. The result: a 125-grain JHP at 1,350–1,450 fps from a 4.49″ barrel, producing roughly 500 ft-lbs of muzzle energy. This combination delivers exceptional barrier penetration and one-shot stop rates in FBI testing. The cartridge was adopted by the US Secret Service, several state highway patrol agencies, and numerous other law enforcement agencies specifically because of these terminal performance characteristics.

Glock 31 vs. Glock 17: Why Choose .357 SIG Over 9mm?

The G31 and G17 share the same frame dimensions and 15+1 magazine capacity, so the choice comes down purely to caliber preference. The .357 SIG offers significantly more velocity, flatter trajectory, and better barrier penetration than 9mm. The tradeoffs are real: .357 SIG ammunition is substantially more expensive and less widely available than 9mm, recoil is sharper, and muzzle blast is more pronounced. Modern premium 9mm loads have narrowed the terminal performance gap considerably. For a shooter whose primary goal is maximum barrier penetration and the flattest possible trajectory from a semi-automatic, .357 SIG remains genuinely superior. For most defensive and duty applications, modern 9mm +P achieves comparable terminal performance with less recoil and at lower cost.

G31 vs. Glock 22: .357 SIG vs. .40 S&W on the Same Frame

The Glock 22 (.40 S&W) and Glock 31 (.357 SIG) share the same frame and many components. A G22 can be converted to .357 SIG with a barrel swap alone—the magazines are compatible between the two calibers, making the conversion inexpensive and reversible. Many G22 owners keep a .357 SIG barrel on hand for this reason. The .40 S&W produces more felt recoil due to its slower, heavier bullet; the .357 SIG produces a sharper snap with its faster, lighter bullet. Both are significantly snappier than 9mm. If you already own or are considering a G22, a .357 SIG barrel gives you both calibers in one platform.

Law Enforcement History and the G31’s Track Record

The Glock 31 has an extensive law enforcement service record. The US Secret Service issued it as a primary sidearm for years. State agencies including Delaware State Police, New Mexico State Police, and Virginia State Police have issued .357 SIG Glocks. The cartridge’s reputation for consistent one-shot stop performance in actual shootings—documented in peer-reviewed law enforcement data from the late 1990s and 2000s—drove adoption by agencies seeking maximum effectiveness. This real-world track record gives the G31 a level of validated performance data that many more modern calibers lack.

Glock 31 Accessories and Aftermarket Support

The G31’s frame is shared with the G17 and G22, so most aftermarket holsters, grip modifications, and accessories for those models fit the G31. Trigger upgrades, night sights, and optic cuts work the same way as on other full-size Glocks. .357 SIG-specific aftermarket is limited to barrels—a threaded .357 SIG barrel from Lone Wolf or Agency Arms is available for suppressor use, though the cartridge’s high velocity makes subsonic loads impractical. The G31’s primary accessory advantage is the easy caliber conversion: a .40 S&W barrel and a 9mm conversion barrel (with a 9mm magazine) both work in the G31 frame.

Related Pages

Browse all Glock firearms, shop .357 SIG ammunition, or explore the compact Glock 32 for a more carry-friendly .357 SIG option.