The RMR footprint is the larger mounting pattern used by full-size optics-ready pistols, and the RMSc footprint is the narrower pattern cut into slim and micro-compact slides. An optic built for one will not bolt straight onto the other, so match the footprint to your slide before you look at anything else.
There is a third pattern that trips people up: Holosun's K footprint, used on the 507K, 407K and EPS Carry. It is close to the Shield RMSc but not identical, which is why Holosun packs an RMSc-to-K adapter plate with several of its K-footprint sights.
Key takeaways
- The RMR footprint was set by the Trijicon RMR. Trijicon's SRO, RCR and RMR HD use it, and so do Holosun's 507C, 407C, 508T and 507COMP.
- The RMSc footprint (from the Shield RMSc) is the slim-slide pattern. SIG's ROMEO-X Compact and Holosun's EPS CORE mount to it directly.
- Holosun's K footprint is close to the RMSc but not the same. The EPS Carry mounts to K directly and comes with an RMSc-to-K plate.
- An RMR-footprint optic will not fit an RMSc cut, and an RMSc optic will not fit an RMR cut, without the right adapter plate.
- Check your pistol maker's documentation or the plate kit before you order. Our model-by-model chart is the next step.
What a footprint actually is
A footprint is the pattern of screw holes and recoil bosses (the small studs or recesses that take recoil load off the screws) on the underside of a red dot, together with the outline of the base. The slide, or the adapter plate on it, has to be cut to the same pattern. If the holes line up and the bosses seat, the optic fits. If they don't, it doesn't, however similar the two sights look.
There is no single industry standard. A handful of patterns dominate, and most of them are named after the optic that set them. For pistols, the two you will meet most often are the RMR and the RMSc.
The RMR footprint
The RMR footprint comes from the Trijicon RMR Type 2. It is the most widely supported pattern on full-size optics-ready pistols and on rifle offset mounts. Trijicon's spec sheet lists the RMR body at about 46 × 28–30 × 25 mm with a 22 × 16 mm window.
A lot of other optics share it, which is the point of a common footprint:
- Trijicon: the SRO (Trijicon sells a single "RMR and SRO" adapter plate), the enclosed Trijicon RCR, which Trijicon launched as a sealed pistol dot "with the RMR footprint", and the RMR HD, which was designed to fit the same footprint as earlier RMRs.
- Holosun: the Holosun HS507C X2 and X3, the 407C, the titanium 508T and the large-window 507COMP. Holosun lists every one as RMR footprint.
- Primary Arms: the SLx RS-10R, which carries the footprint in its product name.
Many full-size optics-ready pistols take RMR-footprint optics through an adapter plate rather than a direct cut. Trijicon's own RMR footprint mounting kit is listed for Glock MOS, Springfield OSP and Prodigy, Walther PDP and H&K VP9 optics-ready slides, which shows how common that route is.
The RMSc footprint
The RMSc footprint takes its name from the Shield RMSc. It is shorter and narrower than the RMR, so it suits single-stack and micro-compact slides where an RMR-sized cut would leave no metal either side.
SIG builds the SIG ROMEO-X Compact on the Shield RMSc footprint and says it is designed for the P365. Holosun's EPS CORE is sold as a direct-mount RMSc optic that needs no plate. Airsoft replica slides cut to this pattern accept the same optics, because the optic only cares about the cut.
Holosun's K footprint: nearly RMSc, not quite
Holosun's micro sights use what it calls the K footprint. That covers the Holosun HS507K X2, the 407K, the EPS Carry and, somewhat surprisingly, the full-size EPS.
The K pattern is close to the Shield RMSc, and the two often get treated as one. Holosun's own packaging says otherwise. The Holosun EPS Carry is listed as K footprint with an RMSc-to-K adapter plate in the box, and the full-size EPS comes with an RMR-to-K plate. If your slide is cut for the RMSc, check whether the K optic you want needs that plate. If you would rather mount straight to an RMSc cut, choose a sight Holosun or SIG list as RMSc.
RMR vs RMSc at a glance
| RMR footprint | RMSc footprint | Holosun K footprint | |
|---|---|---|---|
| Set by | Trijicon RMR | Shield RMSc | Holosun 407K / 507K |
| Typical slide | Full-size and compact double-stack, usually via a plate | Slim single-stack and micro-compact | Slim slides, directly or via Holosun's RMSc-to-K plate |
| Optics we stock | Trijicon RMR Type 2, RMR HD, SRO, RCR; Holosun 507C, 407C, 508T, 507COMP; Primary Arms SLx RS-10R | SIG ROMEO-X Compact; Holosun EPS CORE | Holosun 507K, 407K, EPS Carry, RONIN EPS Carry, EPS, SCS Carry |
| Window (examples) | RMR Type 2: 22 × 16 mm; 507C X2: 0.91 × 0.63 in | EPS CORE: 0.90 × 0.63 in | 507K X2 and EPS Carry: 0.77 × 0.58 in |
Window figures are the makers' published numbers. Holosun quotes inches: 0.91 × 0.63 in is about 23 × 16 mm, and 0.77 × 0.58 in is about 20 × 15 mm. The smaller window is the price of a sight that doesn't overhang a narrow slide.
Expert tip
Before ordering, lay the plate or slide cut next to the optic maker's footprint drawing and count the recoil bosses as well as the screw holes. Screw spacing that matches while the bosses don't is the most common "it nearly fits" mistake, and forcing it is how screws shear.
How to find your footprint
- Check the pistol maker's documentation. Optics-ready pistols say which footprint the slide is cut for, or which plates come in the kit.
- Read the plate. Adapter plates are usually marked with the footprint they accept.
- Match the model, not the brand. Holosun makes RMR, K and 509T footprint optics, and SIG uses Shield RMSc on the ROMEO-X Compact and DeltaPoint Pro on the ROMEO-X Pro.
For every pattern we stock, mapped model by model, see the pistol red dot footprint compatibility chart. For which sight to put on it, see our best pistol red dot sights guide, or the compact slim-slide red dot guide if yours is a micro-compact.
Footprint and emitter are separate choices
Open and enclosed emitters are available on each footprint. On RMR you can choose between the open RMR Type 2 and the sealed RCR. On K you can choose between the open 507K and the sealed EPS Carry. Pick the footprint that fits the slide, then decide whether you want the emitter sealed against rain and grit. Our enclosed vs open red dot guide covers that trade-off. The enclosed red dot sights collection has every sealed option we carry.
UK note
In England, Wales and Scotland most handguns are prohibited under section 5(1)(aba) of the Firearms Act 1968, which covers any firearm with a barrel under 30 cm or an overall length under 60 cm. In Britain, pistol optics are mainly bought for airsoft replicas, long-barrelled pistols and pistol-calibre gallery rifles, and by holders of Section 5 authority. Northern Ireland has its own law, the Firearms (Northern Ireland) Order 2004, whose list of prohibited weapons has no equivalent general ban on short firearms. Confirm your own position with your firearms licensing department.
Frequently asked questions
Can I put an RMSc optic on an RMR-cut slide?
Not directly, because the hole spacing and outline differ. You would need an adapter plate that accepts the RMSc pattern on top and fits your RMR cut underneath. Plates add height, so check your iron sights still co-witness.
Is the Trijicon RMR HD the same footprint as the RMR?
Yes. The RMR HD was designed to fit the same footprint as earlier RMRs, so it uses the same RMR-pattern cuts and plates. Its body is a different shape, so still check it clears your rear sight.
Will a Holosun 507K fit a SIG P365?
The P365 is cut for the Shield RMSc pattern, and the 507K uses Holosun's K footprint, which is close but not identical. Check your slide and the optic's instructions. If you want a guaranteed direct fit, SIG's ROMEO-X Compact is built for the P365.
Which footprint is tougher?
Neither pattern is inherently tougher. How long a sight lasts depends on the optic's housing and on correct mounting: clean threads, the right screws, thread locker and the maker's torque figure.
Shop this guide
- RMR Footprint Red Dot Sights — for full-size slides and RMR-pattern plates
- RMSc Footprint Red Dot Sights — slim-slide optics, including K-footprint Holosuns
- Trijicon RMR Footprint Mounting Kit — puts an RMR-pattern optic on Glock MOS, Walther PDP, Springfield OSP/Prodigy and VP9 slides
- Pistol Dot Sights — every pistol optic we stock
