DIY: How to Mount Your Red Dot Sight on Your Pistol

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Last Updated on May 22, 2021.

Writer for Minuteman Review, handgun aficionado and artisan firearms reviewer. 

DIY How to Mount Your Red Dot Sight on Your Pistol

Although pistol red dot sights have long been a staple of many competition shooting disciplines, they have recently grown in popularity for home defense, personal protection, and even concealed carrying.

Today’s shooters understand the advantages that a red dot brings to the handgun. If you’re looking to become one of those shooters, you’ll want to learn how to install a red dot sight on your pistol without the help of a gunsmith.


The Choice of Red Dot

Before learning how to mount a red dot sight on a pistol, it is critical to know which red dot sight model you want.

Your choice of red dot sight model not only determines factors such as glass quality, dot sharpness, adjustment options, size, and weight, but it also determines compatibility with specific mounting points (and, to an extent, corresponding platforms).

There is a wide array of red dot sights for pistols available on the market. Some of the most popular models include the Trijicon RMR, Vortex Venom, SIG Sauer RomeoZero, Burris FastFire, Leupold DeltaPoint, and many more.

No matter which model you choose, make sure it possesses the build quality and features you need before you proceed with purchasing.


Using The Right Platform

Once you have decided which pistol red dot sight you want, you will need to take a look at your handgun and determine if it is “red-dot ready.” There are three main methods for mounting a red dot on a pistol: the cut slide, the rear sight mount, and the accessory rail mount.

Cut slide

A pistol with a cut slide features a milled cut in the rear part of the slide, behind the ejection port. Some cut slides allow for installing a rear iron sight, while others don’t.

The dimensions of the cut on a cut slide determine its compatibility with specific mounting plates, in turn dictating which red dot sights it can accept.

There are three main ways of obtaining a cut slide: 

  • Purchase a pistol with a pre-cut slide (e.g., Glock 40 MOS), making it red-dot ready out of the factory.
  • Buy an aftermarket cut slide and replace your stock slide with it.
  • Send your existing slide to a gunsmith to have it milled to your specifications. 

Service for the latter typically costs $40-$60, although the exact pricing varies depending on the gunsmith, your pistol model, and your location.

Although using a cut slide is typically the most expensive mounting solution, it is also one of the most popular, as it allows you to install your red dot sight as low as possible.

Many concealed carry holsters may feature red dot cuts as well, allowing you to carry your pistol with an optic. This option is one of the main reasons this mounting method has grown popular in recent years.

Rear sight mount

A pistol with a rear sight mount uses the rear sight dovetail as an attachment point for your mounting plate. The advantage of this solution is that you don’t need to use a cut slide or send your existing slide to a gunsmith.

The tradeoff is losing access to your rear sight dovetail, requiring you to use no iron sights. Alternatively, losing access to your rear sight dovetail can require the use of mounting plates with integrated backup sights, which may not be as good as your favorite irons.

Accessory rail mount

A pistol with an accessory rail mount (also known as a frame mount) uses your pistol’s rail as a mounting point, providing you with a length of optics rail hanging over your slide instead of mounting the optic directly on your slide.

This solution is the oldest and bulkiest for pistol optics of any kind (impossible to carry concealed). But it is one of the most stable and least complicated.

The main advantage of an accessory rail mount is stability. Because your red dot sight is anchored to your pistol’s frame, your reciprocating slide will not move the sight back and forth; the only movement comes from the recoil forces.

Another advantage is this method provides you with a standard Picatinny rail, eliminating the need for a mounting plate (but requiring a rifle-style Picatinny rail mount instead).

Although this solution requires you to give up your frame’s accessory rail, most mounts provide you with a secondary bottom rail, allowing you to install the lights and lasers of your choice.


Installation Process

Learning how to mount a red dot sight on a pistol is easy, but the process depends on your mounting system.

If you are using one of the mounting methods requiring a mounting plate, follow these steps:

  • Install a mounting plate compatible with your slide cut or rear sight dovetail. If you’re using a factory red-dot-ready pistol, you may need to unscrew and remove the factory “blank” plate first.
  • Apply a small amount of Blue Loctite or equivalent thread sealant onto your mounting screws.
  • Drive the mounting screws until they fit snugly into the plate.
  • If your red dot sight’s battery compartment can only be accessed from the underside, now is the time to insert (or replace) the battery.
  • Check your sight’s owner’s manual and verify whether your sight needs a spacer or a waterproofing plate. If it does, install it now.
  • Place your red dot sight onto the mounting plate.
  • As with the mounting plate, apply Blue Loctite or an equivalent thread sealant on your sight’s mounting screws, then drive the screws until you get a snug fit.

If you’re using the accessory rail mount process, follow these steps:

  • Install your mount on your rail according to the instructions in your owner’s manual. Some models may require additional support screws.
  • Place your red dot sight onto a Picatinny rail mount or riser.
  • Install your mounted sight on the rail, securing it as you would on a rifle.

Regardless of your installation process, don’t forget to sight in your red dot at an appropriate distance for your desired application and practice shooting with it regularly.


Parting Shots

Shooting a handgun with a red dot sight presents many advantages: aiming is easy and intuitive, no need to worry about sight alignment, and the red dot functions equally well regardless of lighting conditions.

Although it’s easy to see why pistol red dots are so popular, don’t forget it is a battery-powered electronic sight. Batteries can and do fail. Always keep extra batteries on hand, especially if your handgun does not have backup iron sights.