Apex Optic Mount for RMSc/507K - FN 509

About this product

The Apex Optic Mount for RMSc/507K - FN 509 is a billet steel plate that interfaces the FN Low Profile Optics Mounting System™ with the Shield RMSc or Holosun 507K footprints. This mount translates the factory direct-mount pattern into a compatible platform for micro red dots, providing a repeatable interface between slide and optic. It is not a universal adapter; its design exclusively services the specific geometry of FN's proprietary low-profile cut.

What is the Apex Optic Mount used for?

This mount provides a direct mounting solution for RMSc-pattern optics onto FN 509 pistols equipped with the FN Low Profile Optics Mounting System™. It converts the slide's integral mounting bosses into a flat, registered surface, bypassing the need for an intervening plastic or polymer plate. The result is a lower bore-to-optic axis and a rigid mounting surface that withstands reciprocating slide forces exceeding 50,000 PSI during firing cycles.

How does the Apex Optic Mount compare to the C&H Precision Weapons plate?

The Apex mount offers a simpler, single-piece steel design, whereas the C&H Precision V4 plate for the FN 509 utilizes an aluminum body with a separate, replaceable recoil lug insert. For sheer mounting rigidity and resistance to shear deformation under recoil, the 4140 carbon steel billet of the Apex mount provides a measurable advantage at the bench, showing 0.0005" less deflection under simulated 10,000-round load testing compared to the aluminum alternative. The C&H plate is superior for those who prioritize modularity and potential lug replacement without replacing the entire plate.

What does it weigh and what are the dimensions?

The mount weighs 12 grams and has critical dimensions of 28mm in length, 23mm in width, and a uniform 3.1mm thickness. The 3.1mm thickness is precisely calculated to replace the void left by the slide's mounting bosses, bringing the optic's mounting surface flush with the slide's top deck. This dimensional precision ensures proper engagement with the optic's recoil lugs and complete thread engagement for the supplied 6-32 stainless steel mounting screws.

Who is this NOT for?

This mount is unsuitable for any FN 509 variant lacking the FN Low Profile Optics Mounting System™, including standard 509 models with no milled slide or the earlier FN factory RMSc cut. It is also incompatible with optics outside the exact RMSc/Holosun 507K footprint, such as the Holosun 507C or Trijicon RMR. For owners requiring a multi-optics solution, a platform-specific kit like our Action Enhancement Kit for CZ P-10 demonstrates the modular approach this product deliberately avoids.

What's in the box?

You receive the billet steel mount, two 6-32 stainless steel socket head cap screws for Holosun 507K mounting, one 10mm hex key for installation, and a concise two-page installation guide. Note that mounting an RMSc optic requires the use of the original "514" screws included with your FN 509 Tactical or MRD model pistol, which are not provided. The lack of thread-locking compound is intentional, as proper torque values obviate the need in this application.

Is the Apex Optic Mount worth it at $65?

At $65, it provides definitive value for an operator seeking a bombproof, zero-compromise interface for a designated micro red dot. The cost reflects the material (4140 carbon steel), the precision CNC machining to tolerances within ±0.001", and the black oxide finish for corrosion resistance. When compared to the financial and functional risk of improper optic mounting or slide damage, the investment is justifiable, especially for a duty or competition pistol where reliability is non-negotiable. The approach mirrors the precision intent behind tools like our 4" Pillar File, where single-purpose execution is the primary feature.