If you’ve got a Sig Sauer P320 with the RX Pro slide cut and a Holosun 509T red dot, you’ve probably run into the same problem we see a lot at the shop: that optic wasn’t made to bolt straight onto that slide. The factory mounting pattern doesn’t match up, so you’re left with a gap, a wobbly fit, or having to mess with adapter plates that add height and bulk. This steel optic mount from the kit solves that—it bridges the RX Pro cut and the 509T’s footprint, giving you a solid, direct-mount connection without stacking plates. It’s machined from billet steel with a black oxide finish, so it’s tough, low-profile, and won’t rust on you.
Will This Fit My Gun?
- Sig Sauer P320 with factory RX Pro slide cut (includes X-Five, X-Carry, and similar models with that cut)
- Sig Sauer M17, M18, and Legion series slides with the RX Pro pattern
- Works with slides that have the factory Loaded Chamber Indicator (LCI)—no interference
- Designed specifically for the Holosun 509T (not the 507C or 508T—those use a different footprint)
- Does NOT fit standard P320 slide cuts (non-RX Pro) without modification
Key Features
- Machined from billet steel—stronger than aluminum, won’t shear screws under recoil
- Black oxide finish for corrosion resistance and a low-glare look
- Direct replacement for the factory rear sight plate on RX Pro slides
- Maintains factory sight height alignment (if you still have irons forward of the optic)
- Includes necessary screws for mounting (though we recommend blue Loctite anyway)
Install Difficulty: 2 out of 5
This is a straightforward swap if you’re comfortable turning a screwdriver. You’ll need a small hex key (included with most Holosun optics), a torque wrench if you want to be precise (we recommend 15 in-lbs on the screws), and a dab of blue Loctite. No filing, no fitting—just remove the existing plate, drop this mount in, and torque the 509T down. Watch our install video on the product page if you want to see it done step-by-step.
Frequently Asked Questions
Will this mount work with suppressor-height sights?
Yes, in most cases. The mount sits low enough that standard-height and many suppressor-height sights will co-witness through the lower third of the 509T window. Exact height depends on your specific slide and sight set, but we’ve had good luck with Dawson Precision and Sig factory suppressor sights.
Do I need to remove the Loaded Chamber Indicator?
Nope. This mount is cut to clear the LCI on M17/M18 and other factory slides. You can leave it in place—no extra work.
Will this fit a P320 with a non-RX Pro slide cut?
No, it won’t. The RX Pro cut is a specific pattern with four mounting holes in a rectangular layout. If your slide has the standard “Deltapoint Pro” footprint, this mount won’t align. Check your slide’s markings or measure the hole spacing to be sure.
We ship this mount same-business-day if you order by 2 PM Eastern, and it comes with our standard 30-day satisfaction guarantee. If it doesn’t fit your slide, send it back—no hassle. Need help? Call the shop; we’re real people who actually shoot these things.
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