GLOCK is, by any measure, the acknowledged leader in polymer pistol design on this planet. Over the years, GLOCK pistols have morphed from a single, now-iconic design, the G17, to multiple sizes, calibers, generations and configurations. This year brings another design tour de force across sizes, calibers and, by way of Gen4 modularity, configurations. Immediately visually obvious and certainly of most interest from a design and operator perspective is the introduction of the GLOCK Modular Optic System (MOS) Configuration. The G40 Gen4 in MOS Configuration will introduce this system to the GLOCK line of pistols, with other models and calibers following.

There is a great deal to explore in this announcement, so let’s examine the G40 Gen4 in MOS Configuration in detail from the bottom up, so to speak.

Solid Foundation

The G40 Gen4 in MOS Configuration has deep historical roots vis-à-vis the GLOCK line of pistols. To begin with, it could be seen as an evolution of the G20 in10mm AUTO. The 10mm AUTO cartridge is one of the most powerful semi-automatic cartridges generally available today, and the G40 Gen4 in MOS Configuration has a standard magazine capacity of 15 hard-hitting rounds. The magazines are of the Full Metal Lined (FML) design, which means they’ll consistently drop free should a fast reload become necessary. Generally speaking, GLOCK’s polymer-coated magazines are known for their reliability and capacity.

Originally identified as the ultimate defensive pistol round by now-legendary firearms expert and teacher Jeff Cooper, the 10mm AUTO G40 was adopted by the Federal Bureau of Investigation almost a quarter-century ago, which used it in both pistol and submachine gun platforms for a time. The external ballistics are quite impressive, and the cartridge today is used by discerning operators for defense and hunting applications.

Surrounding the standard-capacity 15-round magazine is the large-frame version of the Gen4 design. The Gen4 design is GLOCK’s latest evolution, with enhanced, 360-degree grip texturing, a reversible magazine catch and the GLOCK Multiple Backstrap System (MBS). The more aggressive texturing of the Gen4 design makes it easier to control the G40 Gen4 in MOS Configuration. The new pistol has a 6.02-inch barrel that will, with GLOCK’s cold-hammer-forged rifling for the most precise bullet-to-barrel fit, wring the maximum performance out of the 10mm AUTO cartridge in both power and accuracy parameters.

As with all Gen4 models, the G40 has the MBS system, another positive aspect of the design. The GLOCK can be run with no backstrap attached, which effectively reduces the trigger reach by 2 millimeters. A significant number of operators prefer this “feel,” and the GLOCK functions normally, which is to say with the usual GLOCK reliability.

“In testing, some commercially available 10mm AUTO loadings recorded an average group radius of just over 2.54 inches at 50 yards!”

An alternate setup is to use either the Medium or Large backstraps, which results in a 2- or 4-millimeter increase in trigger reach, respectively. Of specific interest to your correspondent is the inclusion of the newest version of the MBS, the extended or “beavertail” version. Offered in both Medium (plus 2 millimeters) and Large (plus 4 millimeters) sizes like the original versions, the extension at the top, where the web of the hand meets the frame, may offer significant advantages.

Next-Gen Slide

The barrel is the “heart,” if you will, of any firearm—and the barrel of the G40 Gen4 in MOS Configuration is a strong heart indeed. GLOCK begins with a high grade of steel and uses the cold-hammer-forging process where the barrel blank, after having a mandrel placed in it, is hit with over 45 tons of force. The mandrel has (for the 10mm AUTO) a hexagonal profile with a right-hand, 1-in-9.84-inch twist rate. The hammer-forging process actually condenses the steel, and GLOCK pistol barrels have been famous for decades for uniformity, durability and accuracy. In testing, some commercially available 10mm AUTO loadings recorded an average group radius of just over 2.54 inches at 50 yards!

To preserve such steel, the major steel components (i.e., barrels and slides) are given GLOCK’s advanced surface-hardening finish. This finish is applied after the pieces are machined, and it totally covers all surfaces, external and internal. Just slightly below industrial diamond hardness, the GLOCK surface hardening gives a flat, dark, non-reflective finish that is highly corrosion resistant.

Another Gen4 design feature, the G40 Gen4 in MOS Configuration’s dual recoil spring assembly seems to reduce recoil, a plus with the powerful 10mm AUTO cartridge. Exhaustively tested, the dual recoil spring assembly is primarily constructed of steel, with two springs instead of the older-generation single spring. Along with a positive influence on felt recoil, the dual recoil spring assembly assures positive functioning and protects components over thousands of rounds fired.

Optics Ready

Finally, we come to the top external surface of the slide, where the new GLOCK Modular Optic System resides. Over recent years, designers and shooters have been installing miniature reflex sights on the slides of pistols for ultra-fast shots.

These electro-optical miniature reflex sights have numerous advantages over traditional pistol sights. The concept of optical sights has been proven over the past 20 years or so, beginning with the victories by IPSC/USPSA shooters in practical pistol competitions and culminating in their usage by elite soldiers in special operations units. There is a definite advantage to having both the target and aiming point appear in the same focal plane, and the G40 Gen4 in MOS Configuration introduces this sighting system to GLOCK pistols. There are multiple manufacturers of these small optical sights, and a challenge facing GLOCK engineers was how to accommodate the different mounting “footprints” of the various sights. GLOCK met this challenge with a precise set of mounting plates onto which can be mounted units from Leupold, Trijicon, C-More and many more.

The result is a GLOCK that is optics ready. It will appeal to “seasoned” shooters, those shooters who may have some challenges visually, operators already familiar with the advantages of the mini optical sights and new shooters who will want to try out this enhanced sighting system.

The G40 Gen4 in MOS Configuration is a powerful yet easy to carry pistol for the outdoorsman and hunter. Designed to give the handgun hunter the ultimate choice in a semi-automatic hunting handgun, the lengthened barrel wrings out the maximum velocity and increases terminal ballistics. With high-performance ammo selected, the 10mm AUTO cartridge is on par with the performance of the .41 Magnum revolver cartridge and has proven to be easily capable of taking game such as whitetail deer, Russian boar and feral hogs.

With this new offering from GLOCK, coupled with traditionally superior GLOCK features and qualities, one could safely dub the GLOCK 40 Gen4 in MOS Configuration a “perfect 10!”

For more information on the G40 Gen4, please visit

This article was published in the Glock Autopistols 2015 magazine. To see the entire issue, please visit

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