First Look: Glock 19 MOS Pistol ( Modular Optic System )

Glock 19 MOS Pistol Review

Glock 19 MOS with Trijicon RMR
Glock 19 MOS with Trijicon RMR

Tom McHale headshot low-res square

USA –-( I suppose Glock 17s and 19s go together like a set of wrenches. One size in the toolkit just isn’t enough.

The Glock 17 Gen 4 is great for duty, recreation, home defense, and competition. With the right holster, there’s no reason you can’t carry one concealed. The Glock 19 is ideal for concealed carry with its ½ inch shorter overall height and .7-inch shorter length.

So, it seems logical that Glock released two new MOS (Modular Optic System) models on both the G17 and G19 platforms.

As with the Glock 17 MOS, the Glock 19 MOS shares identical dimensions and operating specifications. However, in the case of the Glock 19 MOS, the sight radius is identical between the two models.

The Glock 19 MOS also ships with three magazines. These pack 15 rounds each plus one in the chamber.

With that said, there are some obvious differences. Let’s take a look.

The Glock 19 Modular Optic System (MOS)

The MOS models come from the factory with a slot milled out of the top of the slide just forward of the rear sight dovetail. The slot is just about two inches long and maybe 3/16 inches deep if you remove the cover and included optics mounting plates. The gun comes with a “cover” plate installed which basically fills this gap completely, so at a glance, the Glock 19 MOS looks like a regular Glock 19 Gen 4 model, except for the visible seams.

 Glock 19 Modular Optic System Pistol MOS
Glock 19 Modular Optic System Pistol MOS

To mount an optic directly to the slide, you simply remove the cover plate and replace it with one of four included adapter plates. These plates are clearly numbered one to four and are cut with posts and holes specific to a variety of optics mounting systems.

Compatible optics (at this time) include:

For my test of the Glock 19 MOS I used a Trijicon RMR RM01 and mounted it to the G19 MOS using plate number two. Installation took less than a couple of minutes and Glock includes an Allen wrench and extra screws used to remove the cover plate and install the correct adapter plate. Once the right adapter plate in installed, just mount the Trijicon RMR (or optic of your choice) to the plate and you’re off to the races.

Glock 19 MOS Pistol – Grip Adjustments

Like the Gen 4 models, the new MOS comes with backstrap panels. The pistol comes with the permanent grip sized for the “short frame” size and rear mounting backstrap panels attach to the grip to create “medium frame” and “large frame” sizes. Glock includes a longer pin and a pin punch tool to remove the trigger housing pin that passes through the upper rear side of the grip. To increase the grip circumference, just push the trigger housing pin out, rock a backstrap into place, and insert the longer pin to lock it in place.

Glock 19 MOS Backstraps
Glock 19 MOS Backstraps

The Glock 19 MOS comes with a medium backstrap which adds .08 inches to the circumference and a large backstrap that adds .16 inches. The new twist is that there are two of each size. One is a standard backstrap while the other adds a significant beavertail that extends a good quarter inch past the small beavertail built into the frame.

I like the new beavertail backstraps. While I’ve not had a problem with slide bite from Glock pistols, the new shape allows you to get really aggressive with a high grip.

Glock 19 MOS Pistol – Mounting an Optic

I had a Trijicon RMR RM01  model on hand to test with the Glock MOS. The RM01 is the battery powered, fixed intensity red dot model with a 3.25 MOA dot size.

The mounting plate included with the Glock fit perfectly with the RMR. Two “posts” on the front of the plate fit into stabilizing and positioning holes on the bottom of the RMR and the two screw holes line up with screw holes in the Glock provided mounting plate. The installation process is simple. Using the included Torx wrench, remove the cover plate. Next, replace the cover plate with the correct mounting plate for your specific optic. Glock provides shorter Torx mounting screws that you use to mount the plate, so be sure to use those. Once the plate is mounted, then you attach your optic with a separate set of screws.

Glock 19 MOS with Trijicon RMR
Glock 19 MOS with Trijicon RMR

One glitch I ran into was that the Glock mount relies on use of the RMR screws provided by Trijicon. My particular RMR was the hi-mount model, which simply means that the basic RMR is screwed onto a taller Picatinny rail mount. The screws that attach the RMR to the Trijicon high mount are a tad too long to use when mounting the RMR to the Glock plate, so you’ll have to acquire shorter compatible screws. I did not have a basic RMR without the mount, so I can’t verify whether Trijicon includes shorter screws with different packagings of the RMR without the rail mounts. Not a big deal, but it’s something to be aware of so you can plan accordingly.

Once I got the RMR mounted, I noticed that the standard Glock sights won’t co-witness through the RMR window. That’s a preference issue, not a checkmark against the MOS. Some people who switch to an pistol optic want a nice clear view of the relatively small viewing window while others may choose to accept some obstruction from iron sights in return for increased redundancy in case the optic fails. Again, it’s just something to know. If you care about co-witnessing iron sights with your optic, you’ll need to plan in swapping out the Glock factory sights for something a bit taller.

I only had a Trijicon RMR during the time I had the Glock MOS, so I can’t speak to how other makes of optical sights do or don’t co-witness with the MOS.

Carrying the Glock 19 MOS

My big question was, can you carry it? Well, of course, you can carry pretty much anything if you set your mind to it. I wanted to find out if the G19 MOS would work with commonly available holsters and carry scenarios.

Here’s what I found.

The Glock 19 MOS with RMR mounted fit perfectly in my well used CrossBreed SuperTuck Deluxe holster. While the optic came close to interfering with the front belt clip, it didn’t. Considering the forward cant of the mount, the sight did not take up any space as it is positioned under the slide. So, no concealed carry “real estate” was sacrificed with this configuration.

The Glock 19 MOS with Trijicon RMR in a DeSantis Snap Slide OWB holster.
The Glock 19 MOS with Trijicon RMR in a DeSantis Snap Slide OWB holster.

I also tried the Glock 19 MOS with RMR mounted on a couple of OWB slide holsters – an Andrews Custom Leather model and the DeSantis Mini Slide. There were no problems with either of these either.

I did find a bit of trouble with a Milt Sparks VersaMax. The RMR did touch the leather back panel under the forward belt clip just before the Glock was fully seated in the holster.

I think the moral of this very informal and small sample size test is that it’s certainly possible to carry the Glock 19 MOS with an optic mounted concealed, but the devil is in the details.

There are too many possible combinations of optic and holsters to try here, so just try before you commit.

Glock 19 MOS Pistol The Bottom Line

The new Glock 19 MOS is the same model 19 that you know and love, just with a new capability to add optics without cutting up your slide. I found the mount to be solid and versatile. I’m looking forward to spending more time with this configuration.


Tom McHale is the author of the Insanely Practical Guides book series that guides new and experienced shooters alike in a fun, approachable, and practical way. His books are available in print and eBook format on Amazon. You can also find him on Google+, Facebook, Twitter and Pinterest.

  • 25 thoughts on “First Look: Glock 19 MOS Pistol ( Modular Optic System )

    1. Muscle memory will correct the problem, I have no issues with the Vortex Venom. By the way, co-witness the sights will defeat the purpose of buying the (this platform) red dot in the first place. (In my opinion)

    2. I had the exact same experience as Tom stated. I do agree also that it could be possible of obtaining the shorter screws outside of going to Trijicon, but with great caution to ensure proper length and thread size. Personally, Trijicon mounting kit is the simplest way and can be found at most competitive firearm related sites and eliminates the possibility or error.

    3. I am not certain exactly why your your having problem on the Glock 19 MOS. I have had absolutely no difficulty but found the mounting somewhat confusing because the Glock MOS mounting kit only provides the correct screws to properly secure “only” the #2 adapter plate to the Glock 19 MOS slide. The shorter screws required to mount the Trijicon RMR to the slide must be obtained elsewhere. There is a caution on the Trijicon website making special note of the obstacle. See Note on the link below:
      Otherwise, I have had no issues with the RMR maintaining accuracy. I really think it is a terrific setup.

    4. Have a glock 10 mm mos worked fine with the RMR bought a glock 19 mos it throws the sight off in about 20 rounds screws and locktight make no difference piss poor design. I am not an beginner once a law enforcement dealer for glock in the state of Iowa and own 18 glocks.

      1. I own a Glock 19 MOS and a Glock 34 MOS both with Trijicon RMRs mounted using the Trijicon RMR mounting kit for the Glock. The Glock screws that mount the #2 Trijicon adapter plate ( provided by Glock) work properly as advertised. However the screws provided by Glock to mount the RMR to the Glock adapter plate “do not”. ( they are too long) The correct screws do come with the Trijicon sealing plate included in Trijicon part# AC 32064.
        Using the setup just described with a touch of Locktight I’ve fired a little over 2600 rounds, half of which was of +P on my Glock 19 MOS w/Trijicon RMR and zero hasn’t moved a bit. My Glock 34 with the same setup has almost 900 rounds through it and it too is perfectly stable. Did you separately purchase the Trijicon manufactured Glock MOS mounting kit, and use it and the DIFFERENT SCREWS that came with this kit to mount the RMR? There is a very real possibility the wrong screws have been used. If that’s the case a tube of Locktight won’t help.
        TJ – US Army Ret.

    5. Tom forgot something entirely with this article … IRON SIGHTS. I have a Glock 19 MOS. When I mounted my Trijicon RMR to the 19 I immediately noticed that use of the iron sights was not possible. To me this is a real problem as I believe all optic systems should have an iron sight backup.
      My solution to this perceived problem was to purchase and install Trijicon’s suppressor sights. They are higher and the weapon may be co-witnessed with the Trijicon reflex sight. … problem solved.
      However, this adds to the problem of finding a holster that will both the MOS and accommodate the higher front sight.

      1. You are correct however, I would use caution configuring the Glock MOS system when blending Trijicon RMR and Supressor sights with Glock MOS optical adapter plates. Earlier in this article someone posted correctly and identified the RMR sealing plate with the “correct” size Trijicon RMR mounting screws. The Glock screws that mount the #2 Trijicon adapter plate ( provided by Glock) work properly as advertised. However the screws provided by Glock to mount the RMR to the Glock adapter plate “do not”. ( they are too long) The correct screws do come with the Trijicon sealing plate included in Trijicon part# AC 32064. Before I mounted the Trijicon Supressor , I emailed Trijicon asking if the GL 201 series Supressor sights would work and co-witness with the Glock 19 MOS. Trijicon technical support confirmed that any of the GL201 variants will work for the Glock 19 MOS. They are taller and I had them professionally installed by a gun smith who had the proper mounting tools.

        1. You’re right. I ran into the problem you describe when I put my setup together.. I called Glock, and I called Trijicon. Glock said it really isn’t their responsibility. Frankly I agree with Glock. They don’t know what is going to mounted on the weapon. Their responsibility is getting the right plate mounted. Trijicon sells you a separate kit to mount the RMR correctly. Finally, with some patience and a bit of lock tight I finally assembled the whole thing, and I really like the setup. 1850 rounds and counting.
          Out here..

    6. Lower mounting is great but there is an expense… Down the road, as sights advance, with the MOS system you simply get a new plate and you’re shooting the new sights. With a dedicated slide you’re stuck with a particular model sight unless you come off the hip again for a new slide and machining costs.

    7. FYI – I bought the DeSantis mini slide for my G19 with RM08G RMR, and I had to modify the holster a little bit to get a full seat. The optic prevented the slide from going all the way in by about 1/4 inch. Concern is that the trigger guard was not completely seated.

    8. I think Glock (and the S&W CORE) dropped the ball by using the plates. A dedicated milled slide is much more usable, as it sets the optic deep enough to co-witness suppressor height sights. With the plate, even these sights sit almost too low for co-witness with the optic. I have been carrying a 26 and a 19 (appendix – IWB) milled for optics since 2011 and will say that co-witness is extremely desirable for this type optic on a defensive pistol. It helps speed up the training curve, as well as having BUIS in the event of optic failure.

    9. This article was very interesting and highly informative, however, after owning a Glock 21, I decided that Glocks were not for me. I’m sure Glock owners will continue to flock to new models, despite the new ones pretty much being the same as the old ones, and the new MOS series will surely generate with many many sales; and this article will help them make the right decision.

      I never did feel comfortable carrying the 21; I was a long time 1911 owner and user, so the Glock was completely foreign territory.

      It shot well, easy to carry, but compared to the standard safety features on a 1911, I found I simply did not trust the Glock.

      Aesthetically, the Glock has always seemed an extremely ugly gun to me, functionally it’s great, but compared to the 1911, the Glock just did not work for me.

      The MOS System looks highly usable, I’m sure that sales will be good, but I’ll pass on Glock; I prefer to carry a pistol that has a number of redundant safety features, because life is never safe nor predictable.

      1. We get it… You don’t like Glock. Why even bother spending the time vomiting your thoughts on this subject? The fact you want a safety has nothing to do with installing an rmr on a Glock. Just move on…

      2. If aesthetics is your need, then by all means go to what you think looks good. However, there are solid facts to support the popularity and reliability of Glock pistols. They are the most common firearm I purchased by police departments throughout the country. There are several factors that support that fact; the foremost is reliability under duress, they are reasonably priced, they work consistently in harsh environments , they offer multiple variants including the MOS systems. Many of the Glock innovations are now on most competitive handgun manufacturers including their trigger design. The new reflex mount offering from Glock with the MOS design works well and is much less expensive than having a slide custom milled. The reflex sight concept is growing in popularity and most major pistol manufacturers are producing competitive alternatives to Glock You have every right to choose which ever firearm that meets your requirements.

    10. Been carrying a Glock 19 Gen 4 for about 6 months. I have other guns I have subcompacts. But I love the 19! It shoots so good. It gives me the capacity I am looking for and fits my hand perfectly. I dont have a problem concealing it. I do with the 17 otherwise I would carry it. I have been waiting for the 19 mos and I will buy one. I have 2 other 19’s as well and 2 17”s who knows may buy the 17 mos too.

    11. I have a Glock 41 mos. I bought a Trificon RM06. I used the Glock #2 mounting plate. Screws with the Trijicon are too long as you stated. Trijicon sales a kit AC32064 to replace the TWO screws for around $20.00. Thank you for giving customers the heads up on Trijicon .

      1. I would love to see Glock include the screws for the supported sights. I didn’t have the opportunity to test all supported sights, so I have to wonder if there are similar issues with any of the others? It’s not like buying two little screws is a big deal, it just brings the installation to a grinding halt unless you know before hand 🙂

      2. had same issue with g19 recently, including my new site flying off the after firing. i was able to fix issue by trip to local ace hardware and purchased 6/32 in x 1/2 in screws with recessed allen heads, ,loctite and no further problems on my g19 m0s. cost of 70 cents. good luck

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