After exploding on the scene in the early 1980s with the GLOCK 17, GLOCK quickly became the benchmark for personal defense, law enforcement, and military handguns. What is not to like about a handgun that is ultra-reliable, accurate, tough, and simple to operate? All at a competitive market price. So, it only makes sense that GLOCK would take it to the next level with the G17L MOS Gen5.
The GLOCK G17L Gen5 MOS
A marketplace review makes it clear that GLOCK is the design standard that the others are still chasing. Detractors would have you believe that GLOCK has grown complacent, resting on its laurels. Many believe the company hasn’t introduced any new designs that depart significantly from Mr. Gaston GLOCK’s original G17 template.
I do not think this is valid, considering GLOCK handguns are currently in their Fifth Generation (Gen5).
A Hidden Gem
What if a de facto “custom” GLOCK, available directly from the GLOCK factory, were available? Let’s define what we mean by custom.
For our purposes here, custom means unique features not ordinarily found on GLOCK firearms. Regarding “GLOCK World”, the G17L and recently introduced G17L MOS chambered in 9MM is the “custom” firearm. Now, before you start calling Smyrna, Georgia, please read further.
The “custom” status I have bestowed on the GLOCK 17L and now G17L Gen5 MOS stemmed from the introduction of the G34. GLOCK’s reasoning, as efficient as their handguns, was that there was no need to continue producing the G17Ls in the same quantity after the G34 was introduced.
The G34 was born from the need to shorten the slide/barrel of the GLOCK 17L to fit size constraints imposed by certain competitive shooting-sanctioning bodies. The dimensions referenced mysteriously follow the classic 1911 pistol.
These market conditions turned the GLOCK 17L into a “de facto custom” GLOCK for US shooters. In effect, the G17L became an “Easter Egg” for knowledgeable GLOCK devotees. For years, anyone fortunate enough to run across a G17L snapped it up because there was no rhyme or reason for its appearance.
It is no accident that the G17L is one of the last GLOCKs to join the Gen5 MOS ranks. I have two Gen3 G17Ls. One was left stock, and the other got a stippling job, new sights, and trigger work.
The focus of this article’s new G17L Gen5 MOS is only sweetening the G17L package by allowing the mounting of a red dot optic.
A Stand-Alone G17
Let’s review what sets the GLOCK 17L Gen 5 MOS (G17L MOS) apart dimensionally and internally from other GLOCK handguns. GLOCK equips it with a 4.5-pound trigger connector, giving the G17L MOS a 5- to 5.5-pound trigger pull with only .5-inch travel. Other GLOCKs have a 5.5-pound trigger connector for trigger pulls measuring 6 pounds or more.
The firing pin and trigger spring enhancements of the Gen5 make it the best out-of-the-box GLOCK trigger to date. The lighter trigger aids accuracy and rapid target engagement. Likewise, the G17L MOS is also equipped with ambidextrous extended slide release levers and a raised/enlarged magazine release button. These are all features that aid in increasing manipulation speeds during reloads.
The G17L MOS’s 6.02-inch barrel is the most obvious departure, giving an overall slide length of 8.85 inches. This is an instance where size does matter. The longer barrel generates more velocity for the 9MM, especially with +P or +P+ loads. GLOCK’s legendary ruggedness enables the use of the higher-pressure 9mm rounds without giving pause for the weapon’s durability.
GLOCK barrels use polygonal rifling versus cut rifling. The polygonal rifling provides a better seal when the bullet obturates when fired down the barrel. This further boosts velocity figures over more typical “land and groove” rifling methods.
Gen5 GLOCKs, including the G17L MOS, benefit from the upgraded GLOCK Marksman Barrel (GMB) with more aggressive polygonal rifling, target-style crown, and tighter chamber specs for enhanced accuracy.
Feeding the G17L MOS
Most factory-listed 9mm velocities are derived from 4-inch barrels. Black Hills Ammunition 124-grain JHP +P and Hornady 124-grain TAP +P 9mm ammunition were chronographed from a 4-inch barrel and then the GLOCK 17L MOS’s 6-inch barrel.
Black Hills Ammunition and Hornady are renowned for consistent velocity, reliability, and terminal performance. The 4-inch barrel generated average velocity figures of 1255 fps and 1137 fps for Black Hills and Hornady loads, respectively. These figures are quite close to factory-listed values.
The GLOCK 17L MOS produced average velocities of 1301 fps and 1236 fps, respectively. Muzzle energy figures have increased 5-8 % with the G17L MOS.
This Is the Way
What if there were ways to maximize the potency of your personal defense handgun? The most obvious personal defense handgun equipment upgrade over the last 15 years has to be red dot sights (RDS). My first articles on red dot use appeared in 2010, thus dating my own journey.
Technology should not be used as a false crutch, substituting for diligent practice and training. However, red dots are definitely a net positive in supplementing the centuries-old iron sight concept. Even with the G17L MOS’s extra-long sight radius of 8.07 inches (a full-size 1911 has a sight radius of 6.8 inches), the GLOCK MOS (Modular Optic System) is a welcome addition to the G17L.
The Trijicon RCR Closed Emitter Red Dot
I mounted a Trijicon RCR closed emitter red dot on the G17L MOS. This was facilitated thanks to the RCR using the same footprint as their standard-setting RMR red dot. The RCR is the evolution of the RMR with a closed emitter ensuring performance no matter the environment. Battery life from the top-loaded CR2023 is six years of continuous use at mid-level brightness setting.
I also installed Meprolight Mepro Tru-Dots suppressor height sights, replacing the factory GLOCK sights. Replacing the G17L MOS front sight revealed another difference between the Gen5 17L MOS and its predecessors.
The nose ring under the front of the G17L Gen 5 MOS’s slide is a polymer nose ring. Simply add pressure to the front of the nose ring and you will be able to move it back to gain access to the front sight screw.
I was eager to get to the range with the G17L MOS/Trijicon RCR combo. The G17L MOS benefits from the longer slide, not just for velocity, but also for the enhanced ergonomic feel/balance. The Trijicon RCR red dot was “there” and seamlessly located from the first draw on. This is a compliment to the GLOCK G17L MOS and Trijicon’s design.
Feel Does Not Mean Fit
One note here of an important lesson relearned. The G17L MOS fit my hand well out of the box (I have average-sized hands). However, the position of the Trijicon RCR dot seemed “high” within the RCR’s frame when presenting the pistol.
Out of curiosity, the medium beavertail backstrap was installed on the G17L MOS. The benefit was immediate! In short, while “feel” is important, proper fit is crucial. Think about how custom rifles and shotguns are contoured to end users. The same applies to handguns, especially ones with red dots.
Proper grip starts from the holster and sets the stage for the most efficient use of a red dot-equipped handgun. The GLOCK beavertail backstraps assisted with intuitively getting my hand in the right place from the start. I didn’t have to adjust after the G17L MOS cleared the holster or, more importantly, after sending some rounds downrange.
The majority of aiming any pistol, red dot or not, is achieved through kinesthetic awareness. Kinesthetic awareness is the body’s knowledge of the relative location and engagement of tension in its parts. This especially pertains to red dots via proper grip and tension applied to the pistol as soon as possible with the shooting hand from the holster and support hand close to the body under the dominant eye.
The grip is the key to tracking the red dot up/down on target during multiple-round drills. The G17L MOS/RCR brought the good vibes in this aspect.
Running an Optic on the G17L MOS
Focusing on the target is one of the key concepts of red dot use. The natural point ability of the G17L MOS comes into its own in this realm. Likewise, the Trijicon RCR did its part as well.
The Trijicon RCR’s rectangular “windshield” offers a superior field of view compared to other red dot options. Correspondingly, the RCR’s lenses are clear with no tinting or other coatings being obvious. The RCR’s minimal frame “disappears” when focusing on the target. Additionally, the crisp red dot displayed no halos or disfiguration.
The G17L MOS combined with the Trijicon RCR proved very capable at quick target engagement. In fact, shots broke faster than it takes to read the description. The G17L MOS’s longer slide/barrel combination contributes more mass, aiding in increased muzzle control for double taps or longer strings of fire.
GLOCK ergonomics combined with the G17L MOS slide’s long track during recoil, mass, and manageable 9mm muzzle signature allows for a very stable sight picture no matter how many or how rapidly rounds are fired.
The G17L MOS eliminated the rectangular slide cut between the breech and muzzle found on the earlier G17Ls. This adds slightly more mass to the slide, which is beneficial.
Shooting the G17L
G17L MOS testing consisted of normal protocol, establishing reliability first, then getting into accuracy and handling. The G17L MOS arrives with three flush-fitting 17-round magazines. GLOCK 24-rd and 33-rd are also readily available.
GLOCK magazines are an often overlooked key component of GLOCK’s legendary reputation for functioning in any imaginable environment. A G17L MOS is not a concealable weapon. It finds itself more at home carried in OWB, tac-vest, or tactical thigh holster with a 33-round magazine handy for a reload.
The G17L MOS takes on a much more serious demeanor when a 33-round magazine is seated with firepower rivaling a submachine gun.
Several magazines worth of ammunition were spent engaging plate racks and man-sized steel targets. No malfunctions were encountered with nearly 400 rounds fired that first day. The G17L MOS is a handgun you can count on being ready to go straight out of the box.
Further range visits only reinforced my fondness for the platform and appreciation for the ability to use the G17L with a red dot now. I will be using the G17L MOS at Echo Valley Training Center’s next Outlaw Steel Match.
The GLOCK Way
It is best to think of the GLOCK line-up of handguns as a “system” stretching from the miniature GLOCK 42 (G42) .380ACP up to the behemoth G40 MOS 10MM. Every GLOCK pays homage to the first G17. Simplicity should not be confused with a lack of refinement. As experience and knowledge expand, GLOCK reliability and solid performance have become more entrenched as the standard.
A day at the range with a GLOCK 17L MOS easily translates into more proficiency with any other GLOCK. Whether it is a G26 tucked inside a belt or a G17L MOS in a tactical thigh rig, it does not require a new manual of arms, only different magazines—sometimes not even that.
The advantage of this is really appreciated when training spans several years and tens of thousands of rounds fired. Intimate familiarization achieved by numerous draw strokes and pressing out to engage the target cannot be overemphasized. The staging and prepping of the GLOCK Safe Action trigger with its short reset can be honed to maximum effectiveness across the many different GLOCK models.
When under stress, this is invaluable. It is difficult to identify any similar handgun models on the market offering the same advantages across a similar range of dimensions and calibers.
It is nice to see the G17L given grudging acceptance and a vote of confidence, with GLOCK offering it in the G17L Gen5 MOS configuration. Anyone who has had the opportunity to experience a G17L often finds themselves re-evaluating GLOCK and the 9mm cartridge.
GLOCK G17L Gen5 MOS Specs
| Caliber | 9mm |
| Action | Semi-automatic GLOCK Safe Action |
| Barrel | 6.02-inches |
| Overall Length | 9.45-inches |
| Weight | 25.4 ounces empty |
| Sights | Adjustable white outline rear and dot front/Trijicon RCR mounted via MOS/Meprolight Tru-Glo suppressor height sights added as well |
| Finish | nDLC |
| Capacity | 3 17-round magazines are included |
| MSRP | $851 |
Performance
| Black Hills 115gr JHP +P | |
| Velocity Avg. | 1322fps |
| Accuracy Avg @ 15yds | 1 inch |
| Winchester 115gr Silvertip | |
| Velocity Avg. | 1268 fps |
| Accuracy Avg @ 15yds | 1.25 inches |
| Black Hills 124gr JHP +P | |
| Velocity Avg. | 1301 fps |
| Accuracy Avg @ 15yds | .75 inch |
| Hornady 124gr TAP FFP +P | |
| Velocity Avg. | 1236 fps |
| Accuracy Avg @ 15yds | .66 inch |
