Best Red Dot Sights for Glock 19 & 17 MOS: Liberty II, Justice II, or Kraken?

The Glock 19 and Glock 17 are some of the most proven fighting pistols on the planet. If you own the MOS (Modular Optic System) version, you have the most versatile platform on the market. But "versatile" can be confusing when it comes to choosing an optic.

Unlike slimline carry guns, the standard double-stack Glock MOS system is built to handle full-size optics. Your decision is less about fitting the gun and more about fitting your individual use case. It also does not matter whether you are running a Gen 4, a Gen 5, or the newer Gen 6 MOS. The plate system carries across all of them, so the optic choice below is the same regardless of which generation you own.

The standard MOS cut uses the RMR footprint via Adapter Plate #02. This opens the door to the two strongest contenders in our lineup: the Liberty II and the Justice II. And for shooters who want maximum environmental reliability, the Kraken closed emitter brings a third path entirely.

Here is how to choose between them.

Liberty II: The Flush Fit

Window Size: 24mm | Footprint: RMR

The Liberty II features a body width that closely mirrors the width of a standard Glock slide. Because the housing does not overhang the sides, it reduces the surface area that can snag on clothing or equipment during a draw.

This optic offers a balance between window size and physical profile. It is the standard choice for concealed carry users who want a capable sighting system that maintains the streamlined dimensions of the pistol.

If your primary use case is concealed carry and you spend most of your time under a cover garment, the Liberty II is the right call. The flush profile lets the gun ride cleaner and draw faster when it counts.

Justice II: The Maximum Field of View

Window Size: 30mm | Footprint: RMR

The Justice II uses the same RMR mounting footprint as the Liberty II but expands the upper lens housing significantly to accommodate a massive 30mm objective lens. This optic prioritizes visibility above all else.

Note that the housing will overhang the sides of the Glock slide slightly. That is the trade-off for gaining the largest possible field of view, and for most duty, home defense, and competition applications, it is a trade-off that's worth making.

Same platform, same mounting system, different mission. Your use case tells you which one belongs on your gun.

Why Window Size Wins Fights

When you step up to a Justice II, you are not just getting "more glass." You are gaining a tactical advantage in recoil management. Here is what that looks like in practice.

Tracking the Dot: Glocks are known for their reliable, flat recoil impulse. A larger window allows you to see that recoil happen in real time. Instead of the dot leaving the window and snapping back, which happens on smaller optics, a 30mm window lets you watch the dot streak up and settle back down without ever losing it. This creates a rhythm that enables faster, more confident follow-up shots.

Unconventional Positions: In a defensive scenario, you might not get a perfect two-handed grip. If you are shooting one-handed, from the ground, or around a barrier, your alignment will not be textbook. A larger window is more forgiving. It lets you find the dot even when your presentation is sloppy. That forgiveness can be the difference when it matters.

The Glock 17 Difference: Full-Size Duty

Most of this guide applies equally to the Glock 19 and the Glock 17, because both run the same MOS plate system and the same RMR footprint. The difference is the platform itself. The Glock 17 is the full-size duty gun, with a longer slide, a longer sight radius, and a grip built for a full firing hand. That extra real estate changes how a red dot rides on the gun.

On a Glock 17 with a red dot, the 30mm Justice II is the natural pairing. The full-length slide carries the larger housing without looking or feeling oversized, and the bigger window plays directly into the Glock 17's role as a duty, home-defense, and range pistol where speed of target acquisition matters more than a slim concealment profile. If you are setting up a Glock 17 MOS, that combination is hard to beat.

That said, plenty of shooters carry a Glock 17, and the flush Liberty II is still the better answer for a concealed full-size gun. The point is that the Glock 17 gives you room to run either optic comfortably. The Glock 19 rewards a more deliberate choice between profile and window size, while the Glock 17 lets you lean into glass without penalty.

Critical Setup Advice: Mounting Your RMR Optic

The following applies to the Liberty II and Justice II. Both mount using the standard Glock MOS system, which is universal, but it requires attention to detail to ensure long-term reliability.

The Plate: Your Glock comes with Adapter Plate #02 for RMR-footprint optics. While this works for casual use, many serious users prefer upgrading to an aftermarket steel plate. Options from C&H Precision or Forward Controls are well regarded, and they give a tighter fit and better thread engagement than the factory MIM (Metal Injection Molded) plate.

The Screws: Use the 6-32 screws provided with your Swampfox optic. Torque them to 15 in-lbs.

Loctite: Always use a small amount of Blue Loctite on the screws. The recoil impulse on a G19 or G17 is snappy, and dry screws will vibrate loose over time. This is not optional for a duty or carry gun.

The Kraken: The Closed Emitter Alternative

If you want to bypass the standard open-emitter design entirely, the Kraken offers a third path that prioritizes maximum reliability above all else.

Window Size: 16mm | Footprint: RMR or Direct MOS

Unlike the Liberty and Justice, the Kraken is a closed emitter optic. The LED is enclosed inside a nitrogen-purged housing sealed with glass on both ends. Rain, mud, lint, or snow cannot block the projection path. If you drop the gun in the mud, you can wipe off the rear lens and keep shooting. That is not a feature you will ever need, until you do.

The In-Box MOS Solution: While many manufacturers force you to buy expensive aftermarket plates to mount a closed emitter, the Kraken includes a dedicated Swampfox MOS Adapter Plate in the box. You do not use the Glock OEM plates or source anything from a third party. Instead, you mount the heavy-duty Swampfox steel plate directly to your slide. The Kraken then clamps onto this plate using a robust side-bolting system similar to a Picatinny rail attachment.

This creates a rock-solid, steel-on-steel connection that bypasses the known weakness of the thin, bendable factory Glock plates. You get a bombproof, sealed optic setup straight out of the package, with no additional purchases and no hunting for compatible hardware.

Quick Comparison

Optic	Window	Emitter	Mounting on Glock MOS	Best for
Liberty II	24mm	Open	RMR footprint via Plate #02	Concealed carry, flush snag-free profile
Justice II	30mm	Open	RMR footprint via Plate #02	Duty, home defense, competition
Kraken	16mm	Closed	Direct MOS, steel plate included	Maximum environmental reliability

All three use the RMR footprint, which means they also fit any RMR-cut Glock slide. For more on which optics share that footprint, see our RMR footprint optics guide.

The Verdict

The Glock 19 and 17 are workhorses. They deserve an optic that matches your mission.

Building a concealed carry rig? Go with the Liberty II. The flush, snag-free profile rides under a cover garment without compromise and gives you a genuine 24mm window on target.

Building a duty gun, nightstand gun, or competition rig? Go with the Justice II. The 30mm window dominates the field of view, tracks the dot through recoil, and forgives an imperfect draw — everything you want when the situation is not ideal.

Prioritizing maximum environmental reliability? Go with the Kraken. The sealed emitter holds up in conditions that will compromise an open-emitter dot, and the included steel MOS plate gives you a mounting solution that is more robust than anything the factory ships with.

All three optics mount directly to your Glock MOS slide. The difference is what you are optimizing for. Make the call based on your use case. The gun can handle whichever one you choose.

If you are setting up a slimline Glock instead, our guide to the best red dots for the Glock 43X and 48 MOS covers the direct-mount approach for those smaller slides.

Frequently Asked Questions

Can you put a red dot on a Glock 19 or Glock 17?

Yes. The MOS (Modular Optic System) versions of the Glock 19 and Glock 17 are cut from the factory to accept a red dot. You install the correct adapter plate, mount the optic, and you are running. Non-MOS Glocks have to be milled by a gunsmith before they can take a red dot, so confirm you have the MOS model first.

What red dot fits a Glock 19 MOS?

Any optic with an RMR footprint fits a Glock 19 MOS using Adapter Plate #02, which includes the Swampfox Liberty II and Justice II. The Kraken mounts directly to the slide using the steel MOS plate included in the box, so it fits the same gun without a factory plate.

Does a Swampfox red dot work on the Glock 19 Gen 5?

Yes. The Glock 19 Gen 5 MOS uses the same MOS plate system as the Gen 4 MOS, so the Liberty II, Justice II, and Kraken all mount the same way. Nothing about the Gen 5 changes your optic choice.

What about the new Glock 19 Gen 6 MOS?

The Glock 19 Gen 6 keeps the MOS plate system, so the same three optics apply. If you are building out a Gen 6, the decision still comes down to use case: Liberty II for carry, Justice II for duty and competition, and Kraken for sealed reliability.

Can you mount a red dot on a Glock 19 Gen 3?

Not directly. The Gen 3 Glock 19 does not have an MOS cut, so the slide has to be milled to accept an RMR-footprint optic like the Justice II. Once it is milled, it runs the same optics as the MOS guns. If you want a bolt-on setup with no machining, start with an MOS slide.

What red dot mounts directly to a Glock MOS slide without a separate plate?

The Swampfox Kraken. Most closed-emitter optics force you to buy a separate plate, but the Kraken ships with a dedicated steel Swampfox MOS plate that bolts straight to the slide, and then the optic clamps to that plate. It is the most direct and most rigid mounting solution in the lineup.

Do you need an adapter plate for a Glock MOS?

For RMR-footprint optics like the Liberty II and Justice II, yes. Your Glock ships with Plate #02 for that footprint, though many serious users upgrade to a steel aftermarket plate for better thread engagement. The Kraken includes its own steel MOS plate, so there is nothing extra to buy.

What is the best red dot for a Glock 17 Gen 5 MOS?

The full-size Glock 17 Gen 5 MOS has the slide length to run the 30mm Justice II without the window feeling oversized, which makes it a strong duty and home-defense pairing. If the gun rides concealed, the flush Liberty II is the better call. Both use the same RMR plate, and the Kraken is there if you want a sealed emitter.

How do you mount and torque a red dot on a Glock?

Use the 6-32 screws that come with your Swampfox optic, add a small amount of blue Loctite, and torque to 15 in-lbs. Skipping the Loctite on a snappy-recoiling Glock is the fastest way to back a screw out, so do not treat it as optional on a carry or duty gun.

Will a Swampfox red dot co-witness with Glock iron sights?

With suppressor-height (taller) iron sights, yes. You can set up an absolute or lower 1/3 co-witness on a Glock MOS. Standard-height factory sights sit too low to appear in the optic window, so plan on a set of tall sights if co-witness matters to you.

Best Red Dot Sights for Glock 19 & 17 MOS (The Duty Guide)