Do Shield RMSc and Holosun K optics share a footprint?
Only partly. The screw pattern matches, the locating posts often do not — and Holosun names its own pattern K rather than RMSc for that reason.
They are treated as the same footprint constantly and Holosun does not call them the same thing. Its own product pages name the pattern "K Footprint" and list fitment as direct mount to that, not to RMSc. Shield originated RMSc, and the two are close enough that the screws line up — which is exactly what makes this look settled when it is not.
The screws are the part that matches. What varies is everything holding the optic against recoil. RMSc-pattern slides differ in how many locating posts they machine and where, and a K optic has recesses for its own arrangement rather than for all of them. So the same optic can seat properly on one RMSc-cut pistol and stand off the posts on another.
| Screw spacing | Matches — which is why it bolts on either way |
|---|---|
| Locating posts | Vary by slide; the K recesses do not cover every arrangement |
| SIG P365 (RMSc cut) | Holosun 407K and 507K seat directly |
| Glock 43X / 48 MOS (RMSc pattern) | Four posts — an adapter plate is sold specifically for this pairing |
That the two pistols above disagree is the whole answer. Both slides are described as RMSc and they are machined differently, so "RMSc" names a family of cuts rather than one cut. A K optic fitting your friend’s P365 tells you nothing about your 43X.
Caution: Check the slide rather than the footprint name. Take the cover plate off and count the locating posts — that, not the label in the listing, is what decides whether an optic seats. Screws alone were never meant to carry recoil.
Sources
- Holosun HS507K-X2 — named as K Footprint, not RMSc
- Shield Sights — the originator of the RMSc pattern
- An adapter plate sold for Glock 43X/48 MOS to Holosun 407K/507K
Last checked 2026-09-03. Specifications change between production runs — verify anything safety-critical against your own firearm and the manufacturer before acting on it.
More on optics and mounting
- Will a Holosun 507K fit a Glock 43X MOS?Usually not without an adapter plate. The screws line up, but the factory cut has four locating posts and a Holosun K optic only clears two.
- What red dot fits a SIG P365 without an adapter plate?Anything cut for the Shield RMSc footprint. The optic-ready P365 slide is milled for it, so RMSc-pattern sights mount straight on.
- Does a Trijicon SRO fit an RMR cut?Mostly. The SRO uses the RMR footprint, but Trijicon requires a mounting kit on Glock MOS, Springfield OSP, Walther PDP and HK VP9.
Have a different question?
Ask TactGPT directly and get an answer written for your specific firearm and setup.
Ask TactGPT