Glock 40 Gen4 MOS


Mounting red dots on polymer handguns is a trend that manufacturers are clearly embracing. Companies like Smith & Wesson, FN. and Sig Sauer, among others. have all introduced optic-friendly models in the last few years. The newest major player to incorporate optics into their handgun lineup is Glock. Earlier this year, the influential Austrian manufacturer rolled out the MOS (Modular Optic System) on their Gen4 series (the 9x19mm G34, .40 S&W G35, .45 ACP G41, and 10mm G40). The heavy-hitting 10mm Glock 40 Gen4 MOS is the subject of this review.

Putting an optic on a handgun is nothing terribly new. Any Bullseye shooter can tell you it’s been done on 1911s, wheel guns, and other firearms for years with the use of special mounts or Picatinny rails. Mounting an optic on a polymer handgun is an entirely different matter. Without a gunsmith making special modifications, such as a machining a divot on your slide, it’s a challenging proposition.

It can also be an expensive endeavor.

Glock has solved this problem by designing a mounting system for production-model pistols. They offer four different base plates that will accommodate a number of popular red dots. These include EOTech, Docter, Insight, Meopta, Trijicon, C-More, and Leupold sights.

I became acquainted with the G40 MOS system earlier this year at an event for firearms journalists called Big 3 East, which was attended by representatives from Glock and other big-name manufacturers.

I liked the G40 for two main reasons: its power and its ballistics. The 10mm Auto round is a stout cartridge with a great deal of kinetic energy. For self-defense purposes, it’s quite formidable. It’s also been popular with hunters pursuing whitetail deer, feral hogs, and similar game. My gunsmith, Brian Takaba of X-Ring Security in Honolulu, reckons that the G40 is the perfect handgun for hunting pigs in Hawaii.

Brian Takaba shows how one of the optic baseplates fit onto the slide.
Brian Takaba shows how one of the optic baseplates fit onto the slide.

That said, hunting isn’t my chief interest. I’m mostly a silhouette shooter and get a kick out of knocking over metal plates and hitting gongs at distances of 100 yards or more. I was curious if I could master shooting this gun at these distances.

A brief history of 10mm

Before we discuss the attributes of the Gen4 G40, a little history of 10mm Auto is in order. The 10mm Auto is not a particularly common cartridge. Even though Glock first introduced a 10mm model (the Glock 20) back in 1991, it’s not a caliber the majority of the shooting public is familiar with.

The 10mm Auto cartridge was developed and championed by Lieutenant Colonel John Dean “Jeff” Cooper, a World War II-era Marine veteran and firearms expert. It was designed to be a medium-velocity pistol cartridge with better ballistics (terminal and otherwise) than .45 ACP. A commercial version was introduced in 1983.

When it first appeared, 10mm Auto seemed like an idea whose time had come. However, the first commercially available gun that was produced to shoot this round, the Bren Ten, had issues—primarily with its magazines. Colt and Smith & Wesson also produced pistols for the new cartridge. In the 1990s, the FBI adopted .40 S&W, effectively a “lighter” version of 10mm Auto, as its standard cartridge (they reverted to 9x19mm in 2014).

Despite the initial attention, law enforcement’s infatuation with the round seemed to quickly dim.

Perhaps it was because police departments were subject to the changing demographics of new hires and 10mm Auto was not a one-size-fits-all solution. Indeed, the 10mm round not only produces a stronger recoil than 9x19mm, but the gun’s grip is on the large side. You need a good-sized hand to get a solid purchase on it. Despite the lack of interest from the law enforcement community, 10mm Auto did attract a following among “civilians.”

Glock’s 10mms

Glock responded to the new 10mm marketplace with two main models, the G20 and G29. The 10mm Auto Glock 40, which is of course the subject of this story, was introduced early in 2015 at SHOT Show. It compares in dimensions with the long-slide, 9x19mm Glock 17L. The long sight radius of the G40 combined with the red dot capabilities and the Gen4 frame distinguish it from other Glock 10mm models. Its full specs, according to the manufacturer, are as follows:

  • Action: Striker-fired, Safe Action
  • Length: 9.49 inches
  • Height: 5.47 inches
  • Width: 1.28 inches
  • Sight radius: 8.19 inches
  • Barrel length: 6.02 inches
  • Rate of twist: 1:9.84 inches
  • Weight unloaded: 28.15 ounces
  • Weight loaded: 40.14 ounces
  • Trigger pull weight: 5.5 pounds
  • Trigger travel: approximately 0.49 inches
  • Magazine capacity: 15

The Gen4 design is the latest 10mm incarnation spawned by Glock. Gen4 characteristics include aggressive, 360-degree grip texturing, a reversible magazine catch, and the Multiple Backstrap System (MBS).

The backstraps included in the Glock 40 Gen4 MOS package.
The backstraps included in the Glock 40 Gen4 MOS package.

Glock’s backstrap system differs from that of other manufacturers. With most other guns you swap out the backstrap to create the ergonomic fit that suits you. With Glock you can only add on to the original size. According to the manufacturer, the stock backstrap (which is integrated with the frame) reduces the trigger distance of the standard size frame by approximately 0.08 inches. The medium-sized back strap adds approximately 0.08 inches (about equal to the size of a standard frame) and the large one increases trigger distance by a total of approximately 0.16 inches.

Another Gen4 feature is a dual-recoil spring assembly that in theory increases the life of the unit and reduces recoil. Constructed from steel, it uses two springs instead of the older-generation, single spring. With the healthy kick of 10mm Auto, reduction of recoil is welcomed. I found the recoil to manageable but not insignificant.

The Gen4 G40’s generous sight radius means with a steady hand you should be better able to hit things at a distance. The longer six-inch barrel also means greater velocity. The round also has a nice, flat trajectory comparable to .357 Magnum.

So what do you get with the G40 MOS kit? A little bit more than you bargained for. When you open the case it practically spills out with odds and ends. These include:

  • Three 15-round magazines
  • Four backstraps (two medium and two large, each available in standard and beavertail)
  • Magazine loading tool
  • Glock MOS mounting plates for red dots
  • Factory test-fired rounds
  • Adjustable sight tool
  • Child safety lock
  • Cleaning brush
  • Docs (manual, warranty, and so on)

Optics ready

Let’s cut to the chase. The coolest aspect of this gun in my opinion is the MOS. Glock has done a great job of integrating the optic with the slide by making it easy to add the red dot. To install an adapter plate, first clear the gun and field strip it. With the slide on a flat surface, remove the adapter cover with special wrench that is supplied with the kit and screw in the appropriate adapter for your optic.

I looked at two optics. The first was the DeltaPoint Pro from Leupold, which retails for about $750, roughly the price of the G40. You can get it on the street for closer to $600 and it comes with a lifetime warranty. Mine was equipped with a 7.5 MOA red delta reticle, which I found easy to use.

Another option is the Burris FastFire III. The FastFire III fits one of the adapter plates perfectly but is not officially supported for the G40. This happens to be an optic that I had on hand and decided to see if I could get it to work with the G40. Brian Takaba helped me shave down the mounting screws and we got it to fit perfectly. Unless you’re willing to do a bit of gunsmithing, I wouldn’t recommend going this route.

A Leupold DeltaPoint mounted on the G40.
A Leupold DeltaPoint mounted on the G40.

It should also be noted that before using the DeltaPoint and the FastFire models, my colleague RN Price and I first tried to install a (10-year-old) Docter red dot. However, it didn’t fit the base plate. Perhaps it was a stretch to expect a decade-old red dot to work on a brand new gun but we figured we might as well try.

Shooting the Glock 40

The G40 MOS offers a gun-and-optics combo akin to love and marriage, soup and salad, or what have you. However, there are a couple of caveats. You’ll want to be certain your hands are big enough to wrap around the grip comfortably. You’ll need to control this big boy to shoot it with any authority.

The key to shooting the G40 any accuracy is the fire control group. It’s much better than the average Glock trigger, but it is not to be confused with a 1911.

It cleanly breaks around five pounds, but the takeup is rather spongy (as you would expect from a Glock). Brian waxed more positively in this regard, comparing the G40 to a slick 1911 race gun. “The only thing missing,” he said, “is the 3.5-pound trigger, which is available from Glock if you want to add it as an aftermarket part.”

The recoil, while not insufferable, is significant—particularly if you’re not used to shooting a magnum-style handgun. I would say the recoil is comparable to a .357 with a stout load. It may be a handful if you’re not used to anything more than a 9x19mm. Muzzle flip, on the other hand, was not a huge issue. One of Glock’s saving ergonomic graces is that it’s designed to place the gun relatively low in the hand. This both reduces muzzle flip and, I would suspect, diminishes the felt recoil.

Glock’s MOS component is a huge improvement over just plain iron sights. The optics option is particularly germane if you’re approaching Social Security age. A red dot makes it so much easier to nail a target, particularly at longer distances. I’ve read that some reviewers have complained that the MOS does not provide for co-witnessing. That’s true, but in my opinion it’s not a valid point.

Anybody who is familiar with Bullseye shooting knows that you don’t need to line up a red dot with an iron sight to be very, very accurate. Sure, it’s a sort of nice-to-have quality, but it’s not mandatory.

For review purposes the ammo we used exclusively was Sig Sauer Elite Performance 180-grain FMJ. Ammo is fairly new to Sig’s repertoire and their 10mm was just introduced this past year.

The author used Sig's 180-grain FMJ load for testing.
The author used Sig’s 180-grain FMJ load for testing.

In our experience, it did everything we could possibly ask of it. There were no jams or failures of any kind and it proved to be incredibly accurate.

According to Sig, the advantage of this bullet’s design is the toothed cannelure which is located halfway up the shank of the bullet. Sig says this location more effectively locks the jacket and lead/alloy core, thus providing “exceptional structural integrity in a jacketed bullet.” The intent is to “ensure maximum weight retention and energy on impact.” We were able to shoot some very respectable groups offhand at 25 yards, including a five-shot group that measured roughly 2.75 inches.

One of the author's better groups, shot at 25 yards offhand.
One of the author’s better groups, shot at 25 yards offhand.

In short, we found this round to be a good match for the G40’s six-inch barrel.

And what about shooting at distances over 25 yards? I hung up gongs at 100 yards and was able to hit discs as small as eight inches in diameter. Hitting a 16-inch gong at this distance proved to be pretty easy. Hitting the eight-inch gong was not so easy, but on a good day I could hit it consistently, which is a testament to its accuracy.

I used targets from Custom Metal Products (CMP). We prefer the CMP-designed gongs because they hold up better than the competition. CMP gongs have holes inside the disc rather than Mickey Mouse-style ears to mount the bolts. I find the latter tend to get blown off sooner rather than later—especially if you’re shooting a 7.62mm rifle. The CMP gongs last longer but even their AR500 hardened steel will eventually crack from 7.62mm abuse (I’ve done it).


The Glock 40 Gen4 MOS is a formidable firearm. It’s accurate and powerful, making it good for hunting or personal defense (though not necessarily concealed carry for obvious reasons). It’s not a target gun and it’s not going to be as accurate as a target gun but I suspect the vast majority of individuals will not outshoot the G40. I’m sure it could be accurized but that’s a subject for another article.

This is definitely not a gun suitable for a novice. It’s simply too much of a handgun. It’s also not appropriate for someone with small hands.

The price may be a consideration for some enthusiasts. This is not you’re your Uncle Ernie’s $400 Glock. The street price of a G40 will run you about $750. This does not include the extra $250 to $600 for an optic.

If you’re an experienced shooter who will make use of an optic-mounted gun that can drop a charging hog or make a gong dance at 100 yards, you’ve come to the right place.

Rob Kay writes a regular column on firearms called On Target Hawaii that is published in a feature magazine called Hawaii Reporter. He recently completed How to Buy an AK-47, a buyer’s guide to the AK platform.

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