Apex Optic Mount for Holosun 509T to Sig P320 RX PRO Cut

This optic mount solves the fitment gap between the Holosun 509T optic and Sig Sauer P320 slides cut with the RX Pro footprint. Rather than modifying the slide or using adapter plates that add height, this component provides a direct, low-profile mounting interface. Machined from billet steel with a black oxide finish, it maintains the optic at the lowest possible deck height while ensuring repeatable zero retention under recoil. Designed for shooters who want the enclosed-emitter durability of the 509T on a factory or aftermarket RX Pro-cut slide without stacking adapter plates.

Compatibility

• Sig Sauer P320 slides with factory RX Pro cut (including X-Series, AXG, and Carry models with that cut)
• Sig Sauer M17 and M18 slides (civilian and military-contract variants)
• Sig Sauer P320 Legion slides (RX Pro cut configuration)
• All P320 slides equipped with the factory Loaded Chamber Indicator (LCI)
• Holosun 509T (all revisions) — direct mount, no additional adapter required
• Does NOT fit standard P320 RMR/Delta Point Pro cuts or older slide generations without the RX Pro footprint

Key Features

• Material: Billet steel, black oxide finish — resists corrosion and wear from holster friction
• Lowest possible optic height: eliminates plate-stacking to keep the 509T close to bore axis
• Precision-machined recoil bosses: prevent optic shift under slide cycling
• Retains factory Loaded Chamber Indicator function: no modification to the LCI assembly required
• Includes necessary mounting screws for the 509T to the mount
• Weight: negligible addition to slide mass — does not affect reciprocating mass balance

Install Difficulty: 2/5

Requires standard hex keys (included), thread locker (Loctite 242 or equivalent), and torque driver capable of 12–15 in-lbs. No slide modification, filing, or fitting required. Remove the factory optic cover plate, place this mount, torque screws per spec, then mount the 509T. Expect 10–15 minutes total.

FAQ

Will this mount work with the P320 M17 that came with the factory Romeo1 Pro?

Yes, if the M17 slide has the RX Pro cut. The Romeo1 Pro uses the same footprint, so removing that optic and installing this mount with the 509T is a direct swap. The LCI remains functional.

Do I need to modify the slide or remove the loaded chamber indicator?

No. This mount is designed to clear the factory LCI on RX Pro-cut slides. No filing, milling, or removal of the LCI assembly is required.

Does this mount co-witness with factory iron sights?

That depends on the suppressor-height sight setup. With standard P320 irons, the 509T will sit low enough to co-witness with taller aftermarket sights. Factory-height sights will not align through the 509T window. Plan for suppressor-height sights if you want a lower-third co-witness.

Shipping & Warranty: Ships within one business day via USPS Priority or UPS Ground. This component carries a limited lifetime warranty against manufacturing defects — no questions asked on fitment issues within 30 days. Return shipping covered on defective units only.