Glock 21 MOS Red Dot Sights – The Ultimate Upgrade for .45 Power

Your Glock 21 MOS is a powerhouse — but adding a red dot makes it even more effective. Whether you’re carrying for defense, hunting, or range precision, a properly mounted red dot improves target acquisition, boosts accuracy, and helps you stay on target under recoil.

At Mounts Plus, we carry a handpicked selection of top-rated red dot sights compatible with Glock 21 MOS Gen 4 and Gen 5. These optics are chosen for their reliability, direct fit options, and ability to handle the hard-hitting .45 ACP.

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Why Add a Red Dot to Your Glock 21 MOS?

The Modular Optic System (MOS) on your Glock 21 allows easy mounting of red dot sights. But with so many optics and mounting styles, it’s crucial to pick the right one.

Benefits of Red Dot Sights for Glock 21:

• Faster sight picture – No need to align front and rear sights

• Better accuracy under pressure

• Improved performance in low-light or aging eyes

• Easier target tracking under recoil

• Modernize your defensive or duty setup

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Direct Mount vs Adapter Plate – Which Is Right for You?

Some red dots mount directly to the Glock 21 MOS slide, while others require an adapter plate. Here’s how they compare:

Feature	Direct Mount	Adapter Plate
Profile	Lower, more natural	Slightly taller
Co-Witness Ability	Better (with low profile sights)	May require suppressor-height sights
Weight	Lighter	Heavier
Durability	Fewer parts, fewer failure points	More pieces to torque and monitor

Pro Tip: If you want the cleanest, strongest setup — go for a direct mount red dot like the Holosun SCS MOS or C&H Precision DMO.

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Top Red Dot Picks for Glock 21 MOS

🔴 Holosun SCS MOS

• Direct mount — no plate needed

• Solar + auto brightness

• Green or red reticle

• Durable, enclosed design

• Perfect for EDC, LE, and outdoor use

🔴 Trijicon RMR Type 2

• Battle-proven ruggedness

• Requires Glock MOS adapter plate

• Adjustable brightness

• Excellent for duty or tactical applications

🔴 C&H Precision Direct Mount Optic

• Enclosed emitter for extreme environments

• Built-in rear sight notch

• Available in red or green

• Machined specifically for Glock MOS footprint

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Which Generations Are Supported?

These red dot sights are fully compatible with:

• Glock 21 Gen 4 MOS

• Glock 21 Gen 5 MOS

All models are factory-cut to support optics — and our options either mount directly or fit using included adapter plates.

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Customer Feedback

“Mounted the Holosun SCS on my G21 Gen 5. Fit was perfect, no plate needed, and sight picture is crystal clear.”
– Mike B.

“Love the low profile of the C&H optic. Easy install, and the built-in rear sight saves space.”
– David R.

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What’s in the Box?

• Red dot optic

• Mounting screws

• Torque or Allen tool

• Battery (if applicable)

• Quick install guide

Installation is easy with basic tools — just add blue threadlocker and follow the torque specs.

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❓ Frequently Asked Questions (FAQ)

Do these sights fit Glock 21 MOS without an adapter plate?

Yes. Some red dots like the Holosun SCS and C&H DMO are designed to mount directly to the Glock MOS slide without a plate.

Can I co-witness these with my iron sights?

You can with suppressor-height sights or optics like the C&H DMO that include a built-in rear sight notch.

Do I need a special tool to install a red dot?

No. All necessary screws and tools are included. We recommend using threadlocker and torqueing to manufacturer specs.

Will these fit Gen 4 and Gen 5 Glock 21 models?

Yes. These optics are compatible with all Glock 21 MOS models with factory optics-ready slides.

What’s the best red dot for Glock 21 recoil?

Both the Trijicon RMR Type 2 and Holosun SCS are proven to hold zero under heavy .45 ACP recoil.