It’s frustrating for gun owners who want to get a red dot optic for their pistol, to find out there are many sizes (footprints) of optics. And many times you need plates or parts to make the optic fit.
So I’ve built this chart to help. It does no good just buying an optic. First you need to figure out what footprint your pistol has, then figure out what optics fit that footprint. From there, you can decide what you’d like to try on your gun.
Once you’ve got your optic, here’s a page to help with installing and sighting it in.
FAT Handguns
Fat guns (as I call them) are double-stack stricter guns. They are perfect for Home Defense, Range Guns, Easier to Shoot.
Fat guns take fatter optics. For Sig they’re called Pro, Holosun they’re called C.
| Pistol Model | Mounting System / Primary Footprint | Direct-Mount Examples | Requires Plate/Pins? | Notes |
|---|---|---|---|---|
| Sig Sauer P320 | Pro-Cut / Romeo1Pro (Delta Point Pro), Sig-Loc (for newer models) | Sig Romeo1Pro, Leupold DPP, Eotech Eflex | No, unless you want to convert to a different footprint like RMR | Varies by exact model; adapter plates common for Holosun 507C / Trijicon RMR. Check your slide cut. |
| Springfield Echelon | Variable Interface System (VIS). Uses cam-pins to take multiple footprints without plates. | RMR, DPP, RMSc, many Holosun models | No plates, but pins from Springfield. | Extremely versatile – one of the most flexible systems. Plates available for ACRO/Docter. |
| Ruger RXM | Modular locator pin system | RMR, DPP, RMSc (Holosun 507C, but can also take K series, etc.) | No plates, but pins from Ruger. | Direct-mount with Ruger pin sets – super flexible like the Echelon. |
| Smith & Wesson M&P 9 2.0 (C.O.R.E.) | Need S&W “CORE” plates | RMR, RMSc, DPP via plates | Yes (S&W plates) | Plates swap easily for almost any popular optic. |
| Glock 17 / 19 / 45 (MOS) | Glock MOS adapter plates | RMR footprint optics (Holosun 507C, Trijicon RMR) | Yes (Glock plates) | Full-size MOS plates are RMR-focused; note: Glock discontinued standard MOS on new Gen 6 CA models. |
Thin Handguns
Thin guns (as I call them) are modern carry guns. They’re not single stack though – They’re like a stack-and-a-half. They’re slim, compact, easy to conceal – for everyday carry.
Thin guns take thin optics. For Sig they’re called Carry, Holosun they’re called K.
| Pistol Model | Mounting System / Primary Footprint | Direct-Mount Examples | Requires Plate/Pins? | Notes |
|---|---|---|---|---|
| Sig Sauer P365 X series (like X-Macro Comp, Fuse, AXG Legion…) | Factory RMSc cut | Holosun 407K/507K/EPS Carry, Sig X Compact, Vortex Defender-CCW | No | Clean direct micro mount. Plates available if you want a larger optic. |
| Springfield Hellcat / Hellcat Pro with OSP Cut | Factory RMSc cut | Holosun K-series, EPS Carry, etc. | Holosun Ks will need this adapter plate or one like it. | Identical RMSc footprint to P365 – huge selection of micro dots. |
| Smith & Wesson Shield Plus 9mm | Factory RMS / RMSc cut | Holosun 407K/507K, Shield RMS, Vortex Defender-CCW | No | Direct RMSc (some models have slight K-pattern tweaks). |
| Glock 43X MOS | Slimline MOS adapter plates | RMSc / micro optics (Holosun 507K, EPS Carry) | Yes (Glock plates) | MOS plates for the slim frame – RMSc-focused. |
| Canik Mete Prime (MC9 series) | Factory RMSc / Holosun K cut | Holosun 407K/507K/EPS Carry, MECANIK MO1 | No | Direct micro mount; very similar to P365/Hellcat. |
Sig Optics
Sig Sauer has a chart to help you with their guns and optics. When you take off your pistol’s plate, you’ll see a series of holes. You can use this chart to identify your exact footprint.
You’ll see that there’s Pro, Sig-Loc Pro (Can do Sig-Lok Pro or Pro), Sig-Loc MHS (Modular Handgun System for the Government), Compact, Sig-Loc Compact (can do Sig-Loc Compact or Compact), Romeo3Max, and finally the older (pre-2010) Romeo1 footprint at the bottom.
You can click this graphic to take you to Sig’s website, where you can then click each footprint to see what optics are available for your gun.
Optics by Brand and Price
Sig Sauer
- Romeo-RS (for Steel Reinforced) is a great but less expensive option, starting at $149. Comes in Pro and Carry versions with multiple recital options.
- Romeo X – Aluminum housing and squared out design for robust strength. Comes in Pro and Carry versions with multiple recital options.
- Romeo X Enclosed – Vacuum sealed to avoid dust, lint, and mud getting into the optic’s projector.
- Sig-Loc – The toughest optics and strongest mounting system so far. Goes in like a ski boot, toe tucks in and back is bolted down. Enclosed as well.
Holosun
- 407 and 507 series – 407 is just a dot. 507 is a circle and a dot. C = Compact (fat), and K = German for small (thin). 507s come in green too, so a circle/dot in green for a thin like a Sig P365 would be “507K Green.”
- EPS – Enclosed, so vacuum sealed front and back to avoid dust, lint, and mud getting into the optic’s projector. “Carry” is for thinner guns (like their K series), and “Core” is their cheaper option. Come in red, green, and gold (sometimes helps color-blind people).
Springfield Prodigy & AOS Plates
The double-stack Springfield Prodigy uses the Agency Arms Optics System (AOS). The plates look like this, with a rear site behind the optic. Depending on the optic you want to use, you need to buy a specific plate to attach it to your Prodigy.
They have a chart on their website to help you buy the right plate for the optic you want to install. But you’ll want to click ‘Details’ because some screws that come with the specific optic will need to be shortened or adapted.
Click this chart to see it on Springfield’s website.
