How to Mount an RMSc Footprint Red Dot on a Glock MOS

Modern pistol optics have become increasingly popular among both competitive shooters and everyday firearm enthusiasts. If you own a Glock MOS pistol and are considering adding a micro red dot sight, understanding the RMSc footprint and proper mounting procedures is essential for achieving reliable performance and maintaining zero.

In this guide, we'll walk you through everything you need to know about mounting an RMSc footprint red dot on a Glock MOS, including compatibility, optic selection, installation steps, and practical tips for co-witnessing your iron sights.

What Is an RMSc Footprint?

RMSc Footprint Explained

Before mounting an optic, it's important to understand the mounting standard your sight uses.

The RMSc footprint was originally developed for slim and compact pistol optics. It features a compact mounting pattern with two recoil lugs positioned at the front of the optic cut. Due to its small size and lightweight design, the RMSc footprint has become one of the most common standards for micro red dot sights used on concealed carry and compact handguns.

Many modern optics—including several popular red dots from VOTATU and other manufacturers—utilize the RMSc footprint because it offers:

• Low-profile mounting

• Lightweight construction

• Faster target acquisition

• Improved concealability

• Wide aftermarket support

Because Glock MOS pistols use adapter plates, understanding the footprint of your optic is critical before installation.

Glock MOS System Overview

The Glock Modular Optic System (MOS) allows shooters to mount various red dot sights using interchangeable adapter plates.

Rather than machining the slide specifically for one optic pattern, Glock MOS pistols provide flexibility through plate systems that accommodate different footprints.

Popular MOS-ready models include:

• Glock 17 MOS

• Glock 19 MOS

• Glock 45 MOS

• Glock 47 MOS

• Glock 34 MOS

This versatility makes MOS pistols ideal for shooters who may want to upgrade optics in the future.

G17/G19 MOS Compatibility

Are RMSc Optics Compatible with Glock 17 and Glock 19 MOS Models?

One of the most common questions shooters ask is about G17/G19 MOS compatibility.

The answer is yes—but typically through the use of a compatible adapter plate.

Most factory Glock MOS plates were originally designed around larger footprints such as:

• RMR

• Docter/Noblex

• C-More

• Leupold DeltaPoint Pro

Since RMSc optics use a different mounting pattern, you'll generally need an aftermarket MOS-to-RMSc adapter plate.

When selecting an adapter plate, look for:

• CNC-machined steel or aluminum construction

• Precise recoil lug engagement

• Proper screw length

• Manufacturer compatibility verification

A quality adapter plate ensures your optic remains secure under recoil and helps maintain zero over thousands of rounds.

Choosing the Right Optic

Open vs Enclosed Optics

Another important consideration when mounting a red dot is deciding between open and enclosed emitter designs.

Open Emitter Optics

Open emitter optics are the most common style found on pistols today.

Advantages include:

• Lightweight construction

• Larger viewing windows

• Lower cost

• Broad product availability

Potential drawbacks:

• Dirt, dust, rain, and debris can block the emitter

• More frequent cleaning may be required

Enclosed Emitter Optics

Enclosed optics completely seal the emitter within the housing.

Advantages include:

• Superior weather resistance

• Improved reliability in harsh environments

• Better protection from mud, snow, and debris

Potential drawbacks:

• Slightly heavier

• Typically more expensive

For everyday concealed carry, many shooters find open optics perfectly adequate. However, duty users and serious defensive shooters often prefer enclosed emitter optics for maximum reliability.

Step-by-Step Guide to Mounting an RMSc Red Dot

Step 1: Verify Compatibility

Before installation, confirm:

• Your Glock is an MOS model

• Your optic uses the RMSc footprint

• Your adapter plate supports both Glock MOS and RMSc standards

Always consult the optic and plate manufacturer's specifications.

Step 2: Gather Your Tools

You'll typically need:

• Torque driver

• Correct mounting screws

• Thread locker (blue Loctite)

• Cleaning cloth

• Isopropyl alcohol

Using proper tools helps prevent stripped screws and mounting failures.

Step 3: Clean Mounting Surfaces

Remove any oil, grease, or debris from:

• Glock MOS slide cut

• Adapter plate

• Optic mounting surface

• Mounting screws

A clean surface allows proper screw tension and prevents movement under recoil.

Step 4: Install the Adapter Plate

Position the RMSc adapter plate onto the MOS slide. Apply a small amount of blue thread locker to the screws and tighten them according to the manufacturer's recommended torque specification. Avoid overtightening, which can damage threads or warp the plate.

Step 5: Mount the Red Dot

Place the optic onto the adapter plate and verify proper seating against the recoil lugs. Install the optic screws and tighten them evenly. Most optic manufacturers recommend torque values between 10–18 inch-pounds, though you should always follow the specific instructions included with your optic.

Step 6: Confirm Function

After installation:

• Rack the slide several times

• Check optic alignment

• Verify screws remain secure

• Ensure the sight picture is unobstructed

Your optic should sit firmly without any movement.

Co-Witness and Mounting Tips

Co-Witness and Mounting Tips for Glock MOS Owners

Proper co-witnessing can significantly improve your shooting experience. A co-witness setup allows your iron sights to remain visible through the optic window, providing a backup aiming solution if the optic fails.

There are generally two co-witness styles:

Lower 1/3 Co-Witness

The iron sights appear in the lower portion of the optic window.

Benefits include:

• Less visual clutter

• Faster target acquisition

• Most popular setup among defensive shooters

Absolute Co-Witness

The iron sights align directly with the optic's centerline.

Benefits include:

• Simplified backup sighting

• Consistent sight picture

Potential drawback:

• More obstruction in the optic window

Additional Mounting Tips

For best results:

• Use only manufacturer-approved screws.

• Verify screw length before installation.

• Recheck torque after your first range session.

• Confirm zero after 100–200 rounds.

• Inspect mounting hardware regularly.

Many shooters experience shifting zero simply because screws loosen over time. Routine inspection can prevent this issue.

Recommended RMSc Optics for Glock MOS Pistols

When choosing an RMSc-compatible optic, look for features such as:

• Shake-awake technology

• Long battery life

• Waterproof construction

• Bright daylight-visible reticles

• Durable aluminum housing

The VOTATU lineup offers several compact pistol optics designed for fast target acquisition and dependable performance, making them suitable options for Glock MOS owners seeking a reliable carry or range setup.

Final Thoughts

Mounting an RMSc footprint red dot on a Glock MOS pistol is a straightforward upgrade that can dramatically improve speed, accuracy, and overall shooting confidence. Understanding the RMSc footprint, ensuring G17/G19 MOS compatibility, evaluating open vs enclosed optics, and following proper co-witness and mounting tips will help you build a reliable optic-equipped handgun.

Whether you're setting up a concealed carry pistol, competition gun, or range firearm, taking the time to properly install and maintain your optic will ensure consistent performance every time you pull the trigger.

Frequently Asked Questions

Can you mount an RMSc optic directly to a Glock MOS?

Not directly. Glock MOS pistols use a universal adapter plate system, and the factory plates are designed for larger footprints such as the RMR or DeltaPoint Pro. To mount an RMSc footprint optic, you need a compatible aftermarket MOS-to-RMSc adapter plate. Once the correct plate is installed, the RMSc optic mounts securely and functions reliably under recoil.

What adapter plate is needed for RMSc on Glock MOS?

You need an aftermarket adapter plate specifically designed to bridge the Glock MOS cut and the RMSc footprint. Look for plates made from CNC-machined steel or aircraft-grade aluminum with precise recoil lug engagement. Several reputable aftermarket manufacturers produce MOS-to-RMSc plates — always verify the plate is rated for your specific Glock model (e.g., G17 MOS vs G19 MOS) before purchasing.

Is RMSc the same as Shield RMSc footprint?

Yes. The "RMSc footprint" refers to the mounting pattern originally established by the Shield RMSc (Reflex Mini Sight Compact). Many optic manufacturers have adopted this same footprint pattern for their compact pistol red dots, making it an industry-standard term. When a product is listed as "RMSc footprint compatible," it means it shares the same mounting hole spacing and recoil lug positions as the Shield RMSc — regardless of the brand.

What are the best RMSc optics for Glock 19 MOS?

The best RMSc optics for a Glock 19 MOS share several key traits: a compact, lightweight profile that doesn't add unnecessary bulk, shake-awake motion activation for instant readiness, a bright daylight-visible dot (3–6 MOA), long battery life, and robust waterproof construction. VOTATU offers RMSc-footprint red dots engineered specifically for compact pistol platforms like the G19 MOS, balancing low-profile design with Mil-Spec durability for both carry and range use.

Should I choose an open or enclosed pistol red dot?

It depends on your primary use case. For concealed carry and range use in controlled environments, an open emitter optic is typically sufficient — it's lighter, offers a wider window, and costs less. For duty use, adverse weather conditions, or high-stakes defensive applications, an enclosed emitter optic provides superior protection against debris, moisture, and fouling. If reliability in all conditions is your top priority, the enclosed design is worth the added weight and cost.