Mount a Red Dot Without Milling the Slide | Guide

It is possible to mount a red dot sight on a pistol without milling the slide, but the correct solution depends on the exact firearm model, its sighting system, the selected mount and the optic footprint. Similar dimensions are not enough: the pistol, mount and red dot must form one fully compatible setup.

This guide explains the differences between a factory optics-ready slide, a conventional adapter plate and a magnetic mount. It also covers RMR, RMSc and DeltaPoint Pro footprints, the advantages and limitations of each system, and the checks that should be completed before using the firearm.

Can You Mount a Red Dot Without Milling the Slide?

Yes. A pistol without a factory optic cut can be fitted with a red dot sight by using a rear-sight dovetail adapter plate or a pistol-specific system such as a CAT Devices magnetic mount.

These solutions avoid permanently machining the slide for a particular optic footprint. However, the factory rear sight will normally need to be removed or replaced, and the mount must be specifically designed for the pistol model.

If you still need to choose an optic, browse our range of red dot sights, where you can compare different sizes, designs and mounting interfaces.

Optics-Ready Slide vs Pistol Without an Optic Cut

Factory Optics-Ready Slide

An optics-ready pistol has a factory-machined recess on the upper surface of the slide. Depending on the manufacturer, the red dot sight may be fitted directly or through a compatible adapter plate.

This arrangement often provides a relatively low and well-integrated mounting position. However, an optics-ready pistol will not necessarily accept every red dot sight. The correct adapter plate, optic footprint, screw length and model-specific compatibility must still be confirmed.

Pistol Without Factory Optic Preparation

If the slide has not been prepared for an optic, there are three main options:

• use an adapter plate fitted into the rear-sight dovetail;
• use a pistol-specific detachable mount, such as a compatible CAT Devices system;
• have the slide professionally milled for a particular optic footprint.

The first two options can allow an optic to be mounted without permanently machining the slide. Milling provides a different type of integration, but it is a permanent modification that should only be performed by a suitably qualified gunsmith.

Red Dot Mounting Systems Compared

Rear-Sight Dovetail Adapter Plates

A dovetail adapter plate uses the factory rear-sight slot to provide a mounting interface for the red dot sight. It is a common alternative when permanent slide machining is not desired.

The underside of the plate must match the geometry of the pistol’s rear-sight dovetail, while the upper side must match the footprint of the optic. Two pistols with visually similar rear sights do not necessarily use the same dovetail dimensions and may require different adapters.

Possible limitations include a higher optic position, removal of the factory rear sight and a less compact installation than a slide specifically prepared for an optic.

CAT Devices Magnetic Mounts: How the System Works

The CAT SM2 system should not be understood as an optic held in position by magnets alone. It combines a pistol-specific mechanical platform with a high-strength magnetic interface, designed to allow a compatible optic to be fitted and removed quickly.

Depending on the pistol, the base of the system may be installed in the position of the factory rear sight. This avoids permanently milling the slide for the red dot footprint, although the rear sight may need to be removed or replaced with a component belonging to the CAT system.

CAT SM2 versions are available for selected configurations of Glock, Glock MOS, Glock Slim, CZ Shadow 2, HK USP Compact and Tanfoglio Stock III. You can compare the available options in our collection of CAT Devices magnetic mounts.

RMR, RMSc and DeltaPoint Pro: Why the Footprint Matters

The optic footprint defines the mechanical interface between the red dot sight and its mount. It determines features such as screw position, locating-lug arrangement and the dimensions of the contact surface.

RMR, RMSc and DeltaPoint Pro are not different names for the same mounting system. They are separate footprints and should only be combined when the manufacturer expressly confirms compatibility or when a suitable adapter is available.

How to Identify the Correct Mount for Your Pistol

Use the following order when choosing an adapter plate or red dot mount:

1. Identify the pistol: confirm the manufacturer, full model name, configuration and generation.
2. Inspect the slide: determine whether it is optics ready, MOS or fitted with a conventional rear sight.
3. Identify the red dot: check its technical specifications for the mounting footprint.
4. Find a pistol-specific mount: it must match both the firearm and the optic footprint.
5. Check additional dimensions: some references distinguish between widths, generations or Slim configurations.
6. Confirm the installation method: establish whether it replaces the rear sight, uses a factory plate or requires a gunsmith.

Do not select a mount simply because it is marked RMR or RMSc. This only confirms the optic-side interface. The underside of the mount must still be compatible with the exact pistol model.

Advantages of Avoiding Permanent Slide Milling

• Reversibility: in many cases, the pistol can be returned to its original configuration.
• Flexibility: an optic can be tested without permanently committing the slide to one footprint.
• Less permanent alteration: no slide material is removed to create an optic cut.
• Future options remain open: the slide is not necessarily restricted to one mounting interface.
• Quick optic changes: certain systems allow the sight to be attached and removed rapidly.

Limitations of Mounts That Do Not Require Milling

Avoiding slide milling can involve compromises. The optic may sit higher, the factory rear sight may need to be removed and compatibility will depend on a specific adapter plate or mount.

With detachable systems, point-of-impact repeatability depends on correct installation, the condition of the contact surfaces and the optic being repositioned according to the manufacturer’s instructions.

No mount should be regarded as universal. It should also never be assumed that the pistol will retain exactly the same point of impact after the optic has been removed and refitted without confirming it at the range.

Safe Installation and Essential Checks

Before working on any mounting system, make sure the firearm is completely unloaded and work in a safe environment. Always follow the instructions provided by the pistol, mount and optic manufacturers.

At a minimum, check the following during installation:

• the mount is intended for the exact pistol model;
• the red dot sight uses the stated footprint;
• the contact surfaces are clean and undamaged;
• the mount is fully seated and has no unwanted movement;
• the screws are the specified type and length;
• the manufacturer’s stated torque values are followed;
• the slide moves freely without interference;
• the optic is correctly aligned and securely mounted.

If installation requires rear-sight removal, specialist tools or fitting work that you cannot perform confidently, use a qualified gunsmith. Incorrect installation can result in unwanted movement, optic damage or a change in point of impact.

Zeroing and Checking the Point of Impact

Once installed, the red dot sight must be zeroed at an authorised shooting range under controlled conditions. Adjust it for the intended distance and use in accordance with the manufacturer’s instructions.

After the first shooting sessions, inspect the mount and confirm that no movement has occurred. If a detachable or magnetic mount is removed and refitted, check the point of impact again before relying on the firearm.

Which Mounting System Should You Choose?

The best solution depends on the pistol, optic and intended use:

• Optics-ready slide: suitable when the pistol is factory prepared and a compatible plate is available.
• Rear-sight dovetail plate: a potentially reversible alternative for selected pistols without an optic cut.
• CAT SM2: a pistol-specific option for a quickly detachable optic without permanently milling the slide.
• Professional slide milling: a permanent option for directly integrating a particular footprint.

For other optic mounting solutions, browse our range of mounts, bases, rings and rails.