Which red dot actually fits your pistol
There is no industry standard for optic footprints. The patterns that exist, the screw threads that ruin slides, real torque numbers, and why we dry-fit.
Here is the thing nobody says out loud: there is no industry standard for mounting a red dot to a pistol. SAAMI publishes standards for cartridges and chambers. It publishes nothing for optic footprints. Every pattern you have heard of is one manufacturer’s proprietary design that other companies then copied, with varying degrees of fidelity.
That is not a technicality. It is the reason two optics that look nearly identical underneath will not swap, and the reason this question is harder than it should be.
What a footprint actually is
Two things: where the screws go, and how the optic is kept from sliding under recoil. That second part is what people miss. Most patterns use lugs or bosses — little posts that sit in matching recesses so the screws are not taking the beating by themselves. Get the screws right and the lugs wrong and the optic is being held on by two small fasteners in shear. That is how optics walk loose.
The patterns you will actually meet
- Trijicon RMR. Two rear screws plus two forward recoil bosses. Used by the RMR, RMR HD, SRO and RCR, and by a long list of Holosun models including the 407C, 507C, 507Comp and 508T — Holosun says “RMR footprint” right on those product pages. Note that the RMRcc is not the RMR pattern, and it uses a different screw again.
- Shield RMSc. The dominant micro/carry pattern. Two screws and four recoil lugs. Used by Shield’s own RMSc, the SIG ROMEO-X Compact, Springfield’s HEX Wasp and others. RMS and RMSc are not the same thing despite the names.
- Holosun K. Holosun treats this as its own footprint, separate from RMSc. The clearest proof is that Holosun ships an RMSc-to-K adapter plate in the box with the EPS Carry and SCS Carry. A company does not include an adapter between two patterns it considers identical.
- Docter / Noblex. Two central screws, four corner sockets, and a separate recoil plate that takes the load. The original open-emitter Vortex Venom, Burris FastFire and several others live here. If someone hands you a used one with no recoil plate, it is incomplete.
- Leupold DeltaPoint Pro. Four locating posts plus two screws. Metric hardware.
- C-More RTS2 / STS2. Its own thing, with host-specific mounting kits.
- Aimpoint ACRO and Steiner MPS. Structurally different from everything above — a clamped rail interface rather than a screw-and-lug pattern. Steiner explicitly built the MPS to the ACRO footprint, which makes this the closest thing to a shared standard in the closed-emitter world.
The mistake that costs the most: screw threads
This is not theoretical and it is not rare.
- Trijicon RMR, RMR HD, SRO and RCR use #6-32 — imperial. The RMRcc uses #5-40.
- Leupold’s DeltaPoint Pro uses M4 x 0.7 x 15.8mm — metric.
- Holosun ships mixed hardware in one box. A 507K comes with both M4 and M3 screws.
#6-32 and M4 are close enough in diameter to start by hand and cross-thread a slide. That is a slide-replacement mistake made with a screwdriver in about four seconds. The rule is simple: use the screws that came with the optic for that specific gun, and if you are guessing, stop and ask.
The other version of this is a screw that is too long. It bottoms out in a blind hole and the optic feels tight while actually being loose. It will shoot itself off, and it can crack the optic body doing it.
Torque, and the part everyone skips
Manufacturer-published numbers, not internet numbers:
- Trijicon RMR, RMR HD, SRO, RCR — 15 in-lbs. RMRcc — 18 in-lbs.
- Leupold DeltaPoint Pro — 25 in-lbs.
- Aimpoint Acro P-2 to the rail — 3.0 Nm, about 27 in-lbs.
Trijicon’s guidance on thread locker is worth quoting properly, because most write-ups drop the second half: fasteners should get a nylon patch or a drop of medium-strength thread locker on clean threads, except where there are steel inserts in an aluminum substrate.
And the line nobody tells carry-gun owners: Leupold’s own manual says to re-check adapter plate torque every 1,000 rounds. If you carry it, put that on your calendar.
Plates, and the two names worth knowing
When the gun and optic do not match directly, an adapter plate bridges them. C&H Precision and Forward Controls Design are the two most-used makers. C&H indexes its catalog both by firearm and by footprint, which is the closest thing to a lookup table that exists — and even they publish a dry-fitting disclaimer, because tolerances vary between your plate, your hardware, your optic and your slide.
Two things a plate costs you: height, which can break an iron-sight co-witness you were counting on, and another mechanical interface that can loosen. Neither is a reason to avoid plates. Both are reasons to be deliberate.
Bring the gun, not the model name
Three things decide the answer, in this order: the exact slide cut on your gun — generation, caliber and slide width all matter, and on slim Glocks the cut itself changed recently — then the optic’s footprint, then whether you need to co-witness irons.
A couple of live examples of why the model name is not enough. Glock cut a second slim-slide pattern in 2025, so two 43X MOS pistols on the same shelf may not take the same optic. And Vortex now sells an enclosed Venom alongside the original open-emitter one — so “it’s a Venom” no longer tells us what we need to know. Bring the optic or the box.
We stock Vortex, Holosun, Sightmark, Leupold and Trijicon, and we have the guns here to try them against. Bring your pistol and your optic to the shop on Route 112 in Medford and we will dry-fit it on the counter before you buy anything.