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

The Glock 19 and 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.

The Standard MOS cut utilizes 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 is not a compromise — it is a deliberate design choice that 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 utilizes 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 is absolutely worth making.

The comparison photo here shows it clearly: same platform, same mounting system, different mission. The Liberty II sits flush. The Justice II dominates the sightline. 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.

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 — for 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 — no additional purchases, no hunting for compatible hardware.

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.