Red Dot Sight Footprints Explained: RMR, RMSc, Holosun K & ACRO

One of the most common mistakes when buying a pistol red dot is ordering an optic that does not fit the slide. The key is the footprint: the pattern of screw holes and locating posts that an optic uses to mount. Get this right and fitting is simple. This guide explains the main footprints you will encounter.

What is a footprint?

A footprint is the standardised mounting pattern on the bottom of a red dot sight. Optics-ready pistols are milled for a specific footprint, either directly or via an adapter plate. If the optic and slide share a footprint, they bolt straight together.

The main pistol footprints

• Trijicon RMR — the most widely supported full-size footprint, used by the Trijicon RMR and many others. If your slide is RMR-cut, you have the widest optic choice.
• Shield RMSc — a compact footprint designed for slim, single-stack and micro-compact carry pistols. Common on subcompact optics.
• Holosun K — Holosun's compact pattern used by the 407K and 507K, popular on smaller carry guns.
• Aimpoint ACRO — a rugged enclosed-optic footprint with a dovetail-style interface, used by enclosed pistol optics built for hard use.

How to find your footprint

Check your pistol's optics-ready documentation or the markings on the included cover plate. Many optics-ready pistols ship with adapter plates for several footprints. If you are unsure, the slide cut pattern and your manufacturer's plate chart will tell you which optics fit.

When you need an adapter plate

If your optic and slide use different footprints, an adapter plate bridges the gap. Browse our red dot sight mounts for plates and mounting hardware. For RMR-pattern optics on rifles, you will also find Picatinny mounts there.

Next steps

With the footprint confirmed, choose your dot size using what MOA means, decide between open and enclosed in open reflex vs enclosed red dot sights, then shop pistol dot sights. Popular footprint-friendly ranges include Holosun and Trijicon.