Apex Optic Mount for Holosun 509T to FN MRD Pistols

This optic mount provides a direct, single-plate solution for attaching the Holosun 509T to FN 509-series pistols equipped with the FN Low Profile Optics Mounting System™. It eliminates the common problem of stacking multiple adapter plates, which can introduce failure points and raise the optic above the ideal bore axis. Machined from billet steel with a black oxide finish, this mount uses an integrated locking key that interfaces directly with the FN 509 slide—no MRD insert is required.

Compatibility

• FN 509 Compact
• FN 509 Full-Size
• FN 509 Midsize
• FN 509 Tactical
• FN 545 (with FN Low Profile Optics Mounting System™)
• Holosun 509T (all generations)

Key Features

• Direct-fit design – Integrated locking key mounts to the slide without the need for a separate MRD insert or stacking plates.
• Billet steel construction – Provides a rigid, zero-compromise mounting platform that resists flex under recoil.
• Black oxide finish – Corrosion-resistant, low-reflectivity surface compatible with duty and competition use.
• Low-profile height – Maintains a co-witness with standard-height suppressor sights (where applicable).
• Precision CNC machining – Tight tolerances ensure repeatable zero retention after optic removal and reinstallation.

Install Difficulty: 2/5

Requires a #6 Torx driver (T6) and blue Loctite (medium strength). Remove the factory cover plate, position the mount with the locking key aligned, torque optic screws to manufacturer specification (typically 15 in-lbs). No slide modification or gunsmith fitting required.

FAQ

Will this work on the FN 545?

Yes. The FN 545 uses the same FN Low Profile Optics Mounting System™ as the 509 series. This mount fits without modification.

Do I need to use the Holosun 509T’s adapter plate?

No. This mount replaces the Holosun 509T’s own RMR-to-509T adapter plate. The integrated locking key directly interfaces with the FN slide, so no additional plates are stacked.

Can I co-witness with factory iron sights?

Yes, with standard-height suppressor sights. The mount’s height allows a lower 1/3 co-witness on most FN 509 and 545 slides equipped with tall sights.

Shipping: Orders over $99 ship free within the continental US. Warranty: This mount is covered by a limited lifetime warranty against manufacturing defects. Contact our shop for replacement or repair.