Description
FN 509 Midsize MRD 9mm 4″ Barrel Flat Dark Earth
The FN 509 Midsize 9mm 4″ 15rd FDE is a purpose-built concealed carry pistol that now comes from the factory ready for your favorite miniature red dot. FN has upgraded this evolution with their Low Profile Optics Mounting System, letting you mount more than 10 different micro red dots directly to the slide without adapter plates. It’s a flat-shooting, fast-handling sidearm that balances a full-size grip with a compact slide and barrel.
| Manufacturer | FN America |
|---|---|
| Model | FN 509 Midsize MRD |
| Caliber | 9mm Luger |
| Barrel Length | 4 inches |
| Capacity | 15 rounds (two magazines included) |
| Finish | Flat Dark Earth polymer frame, black nitride slide |
| Weight | 26.5 ounces (empty, per manufacturer specs) |
| Condition | New |
Key Features
- FN Low Profile Optics Mounting System – Why it matters: You can direct-mount over ten popular red dot sights (including Trijicon RMR, Holosun 407C/507C, and Leupold DeltaPoint Pro) without aftermarket plates, saving you time and money.
- Improved Slide Serrations and Controls – Why it matters: Deeper, aggressive serrations front and rear give you a positive grip on the slide for press checks or malfunction clears, and the enlarged magazine release and slide stop are easier to hit under stress.
- New Textured Backstraps – Why it matters: Two included backstraps (flat and arched) feature an upgraded texture that locks the pistol in your hand, reducing muzzle flip and helping you stay on target for faster follow-up shots.
- Flatter-Faced Trigger – Why it matters: The redesigned trigger shoe has a wider, more contoured face that spreads the pull weight across your finger, leading to a smoother press and a cleaner break with less overtravel.
- Midsize Frame with 4-Inch Barrel – Why it matters: The 4″ barrel gives you a longer sight radius and better velocity than a subcompact, while the midsize grip conceals easily under a cover garment and still holds 15 rounds.
Who It’s For
This pistol is built for the shooter who carries every day and wants the speed of a red dot without the hassle of a gunsmith or adapter plates. It’s also a fine choice for the bird hunter who needs a reliable sidearm for timber or marsh, and for the competition shooter looking to step into carry optics division on a budget.
Pros & Cons
- Pro: Optics-ready out of the box – direct mount for RMR, Holosun, and others.
- Pro: 15-round capacity in a concealable package.
- Pro: Aggressive slide serrations and improved grip texture.
- Con: Trigger pull weight is around 5.5 pounds – some shooters prefer a lighter trigger for competition, but it’s appropriate for a defensive pistol.
Comparison
| Feature | FN 509 Midsize MRD | Glock 19 Gen5 MOS | SIG Sauer P320 M18 |
|---|---|---|---|
| Barrel Length | 4″ | 4.02″ | 3.9″ |
| Capacity | 15 rounds | 15 rounds | 17 rounds (21-round mag also available) |
| Optics Mount | Direct mount (no plate needed for most) | MOS plate system (adapter required) | Pro-Cut slide (plate needed for RMR) |
| Trigger | Flat-faced, 5.5 lb | Curved, 5.5 lb | Flat, 5.5–6 lb |
| Grip Texture | Aggressive polymer | Medium polymer | Medium polymer with replaceable grip module |
| Price | $694 | $599–$649 | $699–$749 |
FAQ
What red dot sights can I mount directly to the FN 509 Midsize MRD without an adapter plate?
You can direct-mount the Trijicon RMR (all models), Holosun 407C, 507C, 508T, 509T, Leupold DeltaPoint Pro, Aimpoint Acro P-1, and several others. The FN Low Profile Optics Mounting System uses a two-screw pattern that fits most micro red dots designed for RMR or DPP footprints.
Does the FN 509 Midsize MRD come with suppressor-height sights?
Yes – it ships with tall, serrated steel sights that co-witness with most red dots. The front sight has a white dot for fast acquisition, and the rear sight is blacked out to reduce distraction.
Can I use standard FN 509 magazines in this pistol?
Yes. The Midsize MRD accepts all FN 509 magazines, including the 10-round, 15-round, 17-round, and 24-round magazines. The 15-round flush-fit magazine is included.
Is the FN 509 Midsize MRD California-legal?
No – this model is not on the California Roster of Handguns Certified for Sale. It ships with a 15-round magazine, so it cannot be sold to California dealers or residents.
Why Buy From Us
- ✅ Nationwide delivery to all 50 states (where legal)
- ✅ Ships within 1-2 business days
- ✅ 30-day return policy on unused firearms
- ✅ Secure checkout with encrypted payment
Browse more semi-auto handguns or check our FN handguns and concealed carry pistols.
Last updated: April 2026
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