Gun Review: GLOCK G19 GEN4 MOS & G17 GEN4 MOS


GLOCK released their MOS, or Modular Optic System, line of pistols a year ago. With the ability to mount a variety of reflex-style red dot optics to the slide, the GEN4 MOS offerings kicked off with big guns suitable for hunting and competition: the G40, G41, G34, and G35. Building on that success and much to the surprise of, well, nobody, GLOCK has given the MOS touch to two of their most popular pistols, the G19 and the G17. I promised Gaston’s gang that I could keep a secret and got my hands on these guys in early December, immediately turning the G19 into my EDC. . .


As the G19 and G17 are two of the most popular pistol models in the world and are used as a basis for comparison in just about every polymer-framed and/or striker-fired handgun review, plus are already reviewed on TTAG here and here and here, I’m not going to re-review them. These are GEN4 GLOCKs, and they’re functionally identical in every last way to the typical GEN4 G19 and G17, other than the MOS components. It’s a GLOCK. You know exactly what you’re getting. These two have proven to be no exception. MOS, then. . .


Each MOS comes with four mounting plates to fit the most popular reflex sights. I have a 4MOA dot JPoint, which is a great little sight, but apparently isn’t popular enough to warrant an MOS plate of its own or a listing in any compatibility guide. Good news, though, as it fits perfectly on plate #04, which is billed as being for the Leupold DeltaPoint. However, you’ll need to pick up a pair of M4x0.7 or M5x0.7 metric bolts.


From the factory, a blanking plate is installed on the MOS pistols.


It fits nicely and makes the guns look like their non-MOS compatriots. The first step to mounting an optic is to remove that blanking plate.


Once you’ve chosen the correct mounting plate for your optic, use two of the provided bolts to attach it to the slide. GLOCK has already applied the thread locker.


Mount the optic to the plate, and you’re in business.


The mounting plates are serrated to match up with and effectively extend the slide serrations. I haven’t been shy about using the optic for racking the slide, though. It obviously works extremely well for that purpose — lots of purchase — and so far it doesn’t seem to mind.


GLOCK’s complaint folder is overflowing with gripes about the MOS guns’ factory sights. And by factory, I mean the exact same polymer sights that come on the non-MOS versions. They’re too short to co-witness with any of the reflex sights that fit the MOS mounting plates. Well, other than my slim little JPoint…


It’s just barely low enough to allow co-witnessing. Actually, it would be better without the factory rear sight in place, as the JPoint has a rear sight notch molded into it that happens to work pretty dang well with the factory GLOCK front. Plus I tend to prefer an all-black rear sight anyway.

Since co-witness heights will be different with just about every optic out there — all of them (as far as I know) are taller than the JPoint — it makes sense to me that the MOS guns just come with the standard, cheap sights. I’d guess that most MOS owners would replace them no matter what, and taller sights would risk the chance of actually blocking the dot on some optics. At any rate, if co-witnessing is on your checklist then you’ll definitely be exploring the near-limitless GLOCK sight aftermarket.


As mentioned, the G19 MOS has been my everyday carry since early December. It’s likely to remain in that role until summer, when I may or may not switch back to a slim little 9mm single stack job. I picked up a mess of kydex to try out, and so far so great. The Cook’s Holsters IWB with adjustable clip holster (reviewed here) works just as well for the G19 as it does for my other EDCs, and with the larger size of the GLOCK I decided to dive into the deep end of appendix carry with the help of the guys at T.REX ARMS. Their Raptor is imminently concealable, and the Sidecar adds a backup mag to the mix. I also picked up a Fenrir OWB that fits both the G17 and G19. Reviews after I break ’em in further.


While the JPoint’s auto brightness adjustment dims it to near-off when it’s in the dark of IWB concealment, helping the 2032 battery last a few months, any electronic sight can die at the wrong time or break for various reasons. This is why backup sights are so important on a defensive-use firearm and why, in a case like this one, they need to be tall enough to be visible through the lens of the optic.

Well, at least if you want to hit targets at longer ranges. A lot of people are actually slower with a red dot on a pistol than with irons, and Nick reminded me that it’s because they’re waiting to find and center the dot. At typical self-defense ranges, forget the dot and just use the reflex sight’s frame like a ghost ring — if it’s visible inside the screen, you’re on target and well within minute of bad guy. For this sort of use, the ability to align the iron sights doesn’t matter. Live battery or dead, dot or no dot, broken lens, etc, you still have a self-defense sight picture.

But getting back to stretching out the range, if that dot is down then the irons absolutely come into play. That would be a shame, though, as a nice red dot is awesome for accurate shooting with a pistol. Especially with the sights on most self-defense pistols, which are designed for quick acquisition and rough alignment rather than high precision. At 3, 7, or 15 or so yards this is ideal, but move back to 50 yards and the confidence level and speed drop. The 4 MOA dot on this JPoint is fine enough for head shots on torso silhouettes out to 100 yards, even if reliably making those shots is a tough ask. Torso hits, though, are available on tap.


The G19 and G17 MOS pistols are the same GLOCKs we’ve come to know and trust. They do, however, open up a world of optics possibilities that don’t easily exist with the standard models. The addition of a red dot can be a big plus for competition, hunting, self-defense, teaching new shooters, and more. Red dots are as simple as it gets for sight alignment, and the right dot can provide bullseye-hitting confidence out to significantly longer ranges than most of us would attempt with standard pistol sights. These little reflex optics are surprisingly unobtrusive for CCW use, and I expect we’ll continue to see more and more optics-ready pistols from GLOCK and most other manufacturers hitting the market in the future.

Specifications (GLOCK G19 GEN4 MOS and G17 GEN4 MOS)

MSRP: $726 (both models)
Everything Else: Identical to standard G19 GEN4 and G17 GEN4

Ratings (out of five stars)

Accuracy: * * * * *
Compared to the non-MOS versions, the ability to slap a red dot on it ups the accuracy potential. Not the gun’s, per se, but definitely the shooter’s.

Customization: * * * * *
Any GLOCK is going to get five stars here, as the aftermarket support is the strongest in the pistol world. Add the ability to easily mount optics, and the MOS versions are really at five stars-plus.

Overall Rating: * * * *
To preempt freakouts, please remember that the overall rating is not the cumulative total of the ratings above it but, rather, takes into account all aspects of the gun, explicitly rated and otherwise. I’m not the biggest GLOCK fan in the world. I’d likely rank any of them at three stars, and feel free to input * * * for all of the missing categories above. After all, GLOCKs are the standard. But then I’d give ’em a well-deserved fourth star for stellar reliability and durability. Optic or not, the MOS guns still have standard GLOCK triggers, plastic GLOCK sights, GLOCK ergos (GEN4 did improve on that a bit), and BLOCK looks. So four stars it is for a pair of very good guns, one of which is my new EDC.