# Will a Holosun 507K fit a Glock 43X MOS?

**Verdict: It depends**

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.

This is the fitment question that catches people out, because the screws line up. The Glock 43X MOS and 48 MOS slides are cut in the Shield RMSc pattern, and the Holosun 507K uses the same screw spacing — so the optic will bolt on and look mounted. Whether it is actually seated is a different question, and it depends on the posts.

The factory Slim MOS cut has four locating posts machined into the slide, two at the front and two at the rear. They carry recoil so the screws are not the only thing holding the optic in place. A true RMSc-footprint optic has four matching recesses in its underside and drops over all four. Holosun K-series optics have two, and shallower — so on a four-post cut, two posts have nowhere to go and hold the optic proud of the slide. It rocks, and the screws end up clamping it onto two hard points instead of a flat surface.

- **Slide cut** — Shield RMSc pattern, Slim MOS
- **Screw spacing** — Matches — this is why it looks compatible
- **Factory locating posts** — Four (two front, two rear)
- **Recesses on a Holosun K** — Two, shallower
- **Result on an unmodified cut** — Optic sits proud and can rock
- **Usual fix** — Adapter plate made for this pairing

Check your own slide before ordering anything. Take the cover plate off and count the posts. Four posts means you need an adapter plate cut for a Holosun K optic, or a slide machined to remove the extra pair. Two posts means the optic can seat directly. Optics that genuinely are RMSc — the Shield RMSc and SMSc among them — clear all four and mount without a plate either way.

> **Caution:** An optic that rocks under recoil will not hold zero, and the mounting screws are carrying load they were never meant to carry. If the optic does not sit flat against the slide with the screws finger-tight, stop and fix the interface rather than torquing it down.

## Sources

- [Holosun HS507K X2 product specifications](https://www.holosun.com/products/hs507k-x2)
- [Glock G43X MOS](https://us.glock.com/en/products/commercial-firearms/pistols/g43x-mos)
- [Shield Sights — maker of the RMSc the footprint is named for](https://www.shieldsights.com/)
- [C&H Precision adapter plate for this exact pairing](https://chpws.com/product/glock-43x-48-mos-to-holosun-407k-507k-adapter-plate/)

## More on optics and mounting

- [What red dot fits a SIG P365 without an adapter plate?](https://www.tactgpt.app/answers/sig-p365-red-dot-footprint.md)
- [Does a Trijicon SRO fit an RMR cut?](https://www.tactgpt.app/answers/trijicon-sro-rmr-same-footprint.md)

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Last checked 2026-09-02. TactGPT can make mistakes. Always check important info for accuracy. The information it provides is intended for educational purposes only. It does not give legal advice; verify any laws cited. Always follow all applicable laws and safety guidelines.

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