This article originally appeared at AmmoLand.
New from Glock at SHOT Show 2016 is the Glock 17 MOS or Modular Optic System. It’s an evolution from the Glock 17 Gen 4, but with a few new surprises.
From everything I can tell, dimensions of the Glock 17 Gen 4 and Glock 17 MOS are identical. Overall length is 7.95 inches, width is 1.18 inches, and height is 5.43 inches. According to the published specs, the barrel in the MOS is also 4.49 inches long. In fact, the only difference I can see is in the sight radius. The MOS has a sight radius of 6.61 inches versus 6.49 with the Glock 17 Gen 4. Apparently, the rear sight is set just a hair farther back on the slide to make room for the optics mount cutout.
The Glock 17 MOS comes with three 17-round magazines and the standard Glock magazine loading tool. So if you carry them all and add one in the chamber, that’s 52 rounds of 9mm ammunition, certainly enough to give Emperor Bloomberg heart palpitations.
With that said, there are some obvious differences. Let’s take a look.
The 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 or mounting plate. The gun comes with a “cover” plate installed which fills this gap completely, so at a glance, the Glock 17 MOS looks like a regular Glock 17 Gen 4 model, except for the visible seams. Even the slide serrations extend to the cover, so the feel will be the same as a standard Glock when the cover is installed.
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:
Plate 1: Docter, Meopta, Insight
Plate 2: Trijicon
Plate 3: C-More
Plate 4: Leupold
For my test of the Glock 17 MOS, I used a Trijicon RMR RM01 with a 3.25 MOA red dot.
Mounting an Optic
The process of mounting an optic is pretty straightforward. Unlike some other optics ready pistols, there are two levels of fastening stuff together with screws.
First, remove the cover plate over the mounting area using the provided Torx wrench. You’ll notice that the optics adapter plate kit comes with four different plates as mentioned above. It also includes four shorter screws than those that attach the cover plate. You only need two screws, so I presume that two are simply spares. They’re shorter because the mounting plate is only about half as tall as the cover plate. This makes sense because, when installed, the base of the optic will be lower than the top of the slide. Store the longer cover screws somewhere safe in case you ever want to go optics free in the future and re-install the plate.
Next, choose the correct plate and using the shorter screws, fasten it to the slide, again using the included Torx wrench. This is the first degree of fastening.
Next, you’ll remove any rail mounts from your optic and mount that to the adapter plate you just installed. From what I can tell, most, if not all, optics will mount using their own screws as the screw holes in the various plates are different sizes.
I did find myself temporarily stuck when mounting the RMR as the screws that came with my tall mount RMR were too long. Just a heads up – check to make sure you’ve got all the right parts before planning your first range outing.
Shooting the Glock 17 MOS
Using a handgun mounted optic is pretty nifty, but it requires some acclimation. Most first-time optics users will have some trouble “finding the dot” easily. I wish I could remember who gave me this tip, but the best advice I’ve gotten on the topic was to forget the red dot sight is there. Just look for the front sight the way your brain is already conditioned. If you just do that instead of searching for the red dot, it will miraculously move right into your line of sight.
Like anything different, it takes some repetitions, so practice bringing the gun from a low ready up to a proper sight picture and you’ll quickly acclimate.
I noticed right off the bat that the factory sights on the Glock 17 MOS won’t co-witness through the optic, at least not with the RMR. The sights on this model are the standard Glock sights, and they fall below the viewable area through the optic. On the plus side, there are no obstructions that block the optic lens. On the downside, if your optic pukes, you have to resort to aiming along the top of the slide. If it’s important to you to have the co-witness capability, it’s easy enough to swap out factory Glock sights for something a little bit taller.
As we discussed in the Glock 19 MOS first look article, there are some new backstrap inserts with the latest models. Instead of the standard two that increase the grip circumference to medium and large, there are now four backstraps. The additional two don’t offer any new sizes. Rather, they are shaped with dramatically extended beavertails. I tried one out and found that I really liked it. You can jam your firing hand as high as you like without worry of slide bite.
The Bottom Line
I looked at the Glock 19 MOS from a concealed carry perspective and found that it’s not all that hard to carry the new model with an optic installed. Most of the holsters I tried were perfectly compatible. You can certainly carry the Glock 17 MOS too, and many people do carry a G17 or one sort or another. With the taller grip, longer barrel, longer slide, and additional capacity, the Glock 17 MOS will make a great competition or home defense gun too.