Originally introduced in 1998, the Glock 31 was the first of the Austrian armsmaker’s polymer- framed semi-autos designed for the new .357 SIG cartridge, which was developed in the U.S. by munitions designers Michael Bussard and Alan Newcomb in 1994 as an alternative high-powder cartridge for law enforcement use. Bussard explains, “When American law en- forcement agencies found the 9mm lacking in ballistic performance, this cartridge was conceived by the designers as a quick, easy solution to the problem. While several large law enforcement agencies use this cartridge, it remains something of a police specialty.”

The .357 SIG is essentially a .40 cartridge case necked down to 9mm. This provides the additional internal volume for heavier powder charges and higher muzzle velocities than the classic 9mm. The .357 SIG is normally loaded with a 124- to 125-grain bullet, and despite its nomenclature, the .357 SIG uses 9mm (0.355-inch diameter) bullets.

Gun Details

The new Gen4 version of the Glock 31 brings better handling and versatility to this already well- established sidearm. The gun now has adjustable fit for hands of of various sizes through Glock’s innovative, interchangeable full-length backstrap panels, and a larger, easier to use magazine catch. The G31 is a standard-sized Glock model. The .357 SIG model is also available in compact G32 and subcompact G33 versions, the latter ideal for concealed carry and as a backup gun.

The full-sized G31 measures 7.95 inches with the standard backstrap, 8.03 inches with the medium backstrap, and 8.11 inches with the large panel in place. Changing the backstraps adjusts the distance to the trigger from 2.76 inches to 2.83 inches, and 2.91 inches, respectively. This is an all-important feature for the Gen4 version of the .357 SIG, as recoil management is essential with this hard-hitting defensive cartridge. The G31 Gen4 also employs Glock’s new double recoil spring/ guide rod design to help mitigate muzzle flip. There is also a ported-barrel version for enhanced stability and ac- curacy, the Glock 31C Gen4.

Specs for the G31 Gen4 show a factory trigger pull of 5.5 pounds, a weight of 23.28 ounces (empty), and a standard magazine capacity of 15 rounds. There are also 10- and 16-round magazines available. Our test gun came in a bit heavier, with a measured average trigger pull of 6.25 pounds and a length of pull (including the safety toggle) of 0.5 inches. Reset, like all Glock models, is almost instantaneous, and a Glock will fire a chambered round even with the magazine removed.

Standard features on the Gen4 models include a Picatinny rail on the dustcover, which accepts a variety of Glock tactical lights, lasers, and combination laser/ tactical light systems like the GTL 10, GTL 21/22, and GTL 51/52, as well as other Picatinny-mountable accessories.

Range Test

For test purposes, the medium grip panel had the best fit. The attachment is simple. A small tool is included with the grip set to push out the trigger housing pin at the top of the grip frame. The replacement panel completely covers the backstrap. It attaches at the base of the grip frame (magazine well) and is pressed over the standard backstrap, aligning the holes in the panel with those in the grip frame. A longer trigger-housing pin is also supplied and is pressed through the holes to secure The G31 Gen4 also employs Glock’s new double recoil spring/guide rod design to help mitigate muzzle flip.

It takes about two minutes to switch panels. The replacement backstraps have the same stippled texture, so the feel of the grips is not changed, only the curvature and depth of the backstrap. The G31 Gen4 was fitted with fixed tritium front and rear sights. This proved to be a superb combination under all lighting conditions. Glock also offers optional steel sights and adjustable rear sights. With a weight of 33.5 ounces with 15 rounds on board, the G31 Gen4 has excellent balance considering the lightweight polymer frame. For a hand- gun originally designed for 9mm cart- ridges, the Glock is very manageable with .357 SIG rounds traveling down a 4.49-inch barrel. Tests were done firing off-hand from a distance of 50 feet using Speer Gold Dot 125-grain GDHP (Gold Dot hollow point) ammunition. Speer is one of the primary manufacturers in this caliber, which is also produced by Federal, Remington, Winchester, CorBon, and PMC.

The .357 SIG packs a wallop on both the sending and receiving end, clearing the chronograph traps at 1,390 feet per second (fps). Thankfully, the heavy-duty recoil system in the Gen4 model absorbs a remarkable amount of energy, making the .357 SIG’s rebound feel more like a 9mm +P cartridge. The best group measured 1.25 inches for five rounds, with three overlapping.

Final Notes

A Glock is a versatile handgun in any caliber, but when you step up to hot loads like .357s, the stamina of the gun comes shining through with impressively manageable recoil, consistent accuracy, feeding, ejection and a maximum capa- city of 15+1. This is a lot of gun to pack on your hip, but when the situation calls for a high-power defensive cartridge that will get the job done, the .357 is a proven choice both for law enforcement and in the private sector. The Glock 31 Gen4 presents an ideal platform for this cartridge due to its lighter overall weight, rugged construction and history of reliability in the field. For more information call 770-432-1202 or visit

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