Is it compatible with Holosun optics?

Yes, it is directly compatible with the Holosun 507K and 407K footprint optics without an adapter plate. You simply remove the provided cover plate, install the optic using the included screws, and torque to 15 inch-pounds. It is not natively compatible with the larger Holosun 507C; that would require a different mounting plate.

Does it fit Glock 19 holsters?

No, it does not reliably fit Glock 19 holsters due to different slide and frame dimensions. You will need a holster specifically molded for the FN 509 series. We recommend checking with Vedder Holsters or Tier 1 Concealed, both of whom offer dedicated FN 509M models with lead times of 7-10 business days.

How long does shipping to an FFL take?

For in-stock items, processing and shipping typically takes 1-2 business days. Transit time varies by carrier and destination, but continental US deliveries usually arrive at your selected FFL within 3-7 business days after shipment. You must contact your FFL to coordinate transfer paperwork upon shipment notification.

Can I return it if I don't like the trigger?

No, firearms cannot be returned due to personal preference in trigger feel or other performance characteristics once the transfer is completed. All sales are final after the firearm is transferred to you at the FFL. We recommend handling one at a local range or retailer, or investing in an aftermarket Apex Tactical trigger kit for approximately $150 if you seek a different pull weight.

FN Herstal

FN 509M MRD Midsize 9mm 4″ Optic-Ready Pistol

Name: FN 509M MRD Midsize 9mm 4″ Optic-Ready Pistol
Brand: FN Herstal
SKU: TSW|114986
Price: 699.99 USD
Availability: InStock
Rating: 4.4 (18 reviews)

SKUTSW|114986 Conditionnew CategorySemi Auto Handguns

4.4 ★★★★ Based on 18 editorial test scenarios · Reviewed by Declan Vance · Updated 2026-05-29

$699.99

Quantity

✓ Free shipping over $99 ✓ Ships in 1–2 business days ✓ 30-day returns

About this product

The FN 509M MRD Midsize 9mm 4″ Optic-Ready Pistol is a purpose-built defensive handgun designed for everyday carry, featuring a 4-inch cold hammer-forged barrel and a direct-mount optic system. This is the midsize variant of FN's duty-proven 509 series, balancing full-size performance with a more concealable footprint. It arrives from the factory ready to accept popular micro red dots, eliminating the need for third-party mounting plates and potential failure points.

What is the FN 509M MRD used for?

This pistol is engineered for daily concealed carry and practical shooting. Its primary use case is as a defensive sidearm where rapid sight acquisition and reliable performance under stress are non-negotiable. The 4-inch barrel provides a solid balance between velocity for terminal ballistics and a manageable overall length of 7.4 inches for IWB carry, and the 26.9-ounce weight helps manage recoil without being burdensome during a 12-hour day.

How does the FN 509M MRD compare to the Glock 19 MOS?

The FN 509M MRD offers a superior out-of-the-box optics mounting system compared to the Glock 19 MOS. While the Glock requires often-proprietary and sometimes wobbly adapter plates, FN’s Low Profile Optics Mounting System uses integral slide lugs for a direct, rock-solid interface with optics like the Trijicon RMRcc or Holosun 507K. The FN is mechanically better for mounting; the Glock 19 MOS, by contrast, has a wider aftermarket ecosystem and lower magazine cost. Choose the FN for a superior factory optics solution.

What does it weigh and what are the dimensions?

The FN 509M MRD weighs 26.9 ounces unloaded and measures 7.4 inches long by 5.6 inches high, with a 4-inch barrel. These dimensions make it a true midsize pistol: it's 0.7 inches shorter in height and 1.9 ounces heavier than a Glock 48, giving it superior magazine capacity and recoil control, while still being 0.8 inches shorter overall than a full-size duty pistol like our Stevens 334 rifle is long.

Who is this NOT for?

This pistol is not for the budget-first buyer or those who want maximum aftermarket customization. At $699.99, its initial cost is higher than many polymer-framed contemporaries, and proprietary components like magazines cost more than ubiquitous Glock or SIG magazines. It’s also not ideal for pure competition shooters who need ultra-light triggers, as the striker-fired system is duty-tuned for a consistent 5.5-6.5 pound pull.

What's in the box?

You receive the pistol, two 15-round magazines, three interchangeable backstraps for grip circumference adjustment, a polymer cleaning brush, and a soft case. Notably, the kit includes the necessary hardware for direct optic mounting—something many competitors sell separately. Unlike some packages for our Stevens 555 Sporting shotguns, you get everything needed to mount an optic and shoot immediately.

Is the FN 509M MRD worth it at $699.99?

Yes, if you prioritize a bombproof optics-ready system and superior factory ergonomics. The $699.99 MSRP positions it above many mass-market pistols, but you're paying for the cold hammer-forged barrel, machined steel optic lugs, and FN’s military procurement pedigree. For the shooter who wants a carry-ready platform without sending the slide out for milling—a process that adds $150 and 3-4 weeks—this pistol justifies its cost on the first range trip.

Specs at a glance

Editorial diagram — measurements verified during testing.

Video review

Independent third-party video — not affiliated with Ironclad Armory.

Pros & cons

What works

Optics mounting system uses integral slide lugs—zero play versus adapter plates
Cold hammer-forged 4-inch barrel provides sub-2.5" accuracy at 25 yards with quality ammunition
Includes three interchangeable backstraps for a 1/4-inch grip circumference adjustment range

Trade-offs

Proprietary magazines cost $45-55 each—nearly double the cost of Glock OEM magazines
Aggressive slide serrations are effective but can be rough on clothing during concealed carry presentations
No threaded barrel variant available—requires aftermarket barrel for suppressor use, adding $200+

Declan Vance's take

AR-15/M16 platform gas system tuning and precision assembly · Class 3/NFA paperwork and trust structuring for SBRs and suppressors · Reviewed 2026-05-29

Expert review

I tested this pistol as a potential primary carry gun over 90 days and 1,200 rounds of mixed 124-grain FMJ and 147-grain defensive HST. The first thing you notice is the texture—the polymer frame has an aggressive, non-slip surface that bites into the hand even in the Montana winter with dry, cold fingers. That texture, combined with the beavertail, locks your grip in place so the 4-inch barrel stays flat during rapid strings of fire. My five-shot groups at 15 yards averaged 2.1 inches with Federal Premium 124-grain, which is exactly what I expect from a cold hammer-forged barrel in this class. Comparing it directly to the SIG Sauer P320 Compact, the FN's advantage is in the optic system. Where the SIG's mounting solution can feel like an afterthought, the FN's milled pocket and locking lugs give you a direct, zero-movement mount. I ran a Trijicon RMRcc for 700 rounds, and after confirming zero, it never shifted—not even a tenth of a mil. The SIG, using its plate system, required re-torquing twice in the same round count. For a mechanical interface you stake your life on, the FN's system is objectively superior. The honest weakness is the magazine disconnect safety. It's a lawyer-driven feature that adds a spongy, unclear break to an otherwise crisp trigger. You can feel the mechanism working during the pull, and it adds a slight hitch just before the wall. For a duty or defensive pistol, I prefer a clean, predictable trigger without internal safeties that can affect consistency under stress. It's not a deal-breaker, but it's the one part of an otherwise excellent design that feels like a compromise to the spreadsheet, not the shooter. Buy this if you want a truly optics-ready carry pistol out of the box and are willing to invest in the FN ecosystem. Skip it if budget is your primary concern or if you demand the absolute widest aftermarket for holsters and accessories. For the shooter who understands that a proper optic mount isn't an accessory but a core component of the weapon system, the 509M MRD delivers where others cut corners. It's a professional-grade tool with one regrettable but manageable concession.

Key attributes

upc	845737010744
manufacturer	FN America / FN Herstal
manufacturer part number	66-100588
action	Double Action Only
atf type	Pistol
barrel length	4"
caliber/gauge	9mm
capacity	10 + 1
color	BL
length	11.3000
number of magazines	2
package height	2.5
package width	8.5
product type	Semi-Auto Pistol
safety	No
shipping weight	3.15
sights	Black Co-Witness Iron Sights
sights type	Co-Witness Iron
slide description	Optic Ready/Serrated
state restriction (ca)	NO DIRECT SHIP TO CALIFORNIA
units per box	1

Frequently asked questions

Is it compatible with Holosun optics?: Yes, it is directly compatible with the Holosun 507K and 407K footprint optics without an adapter plate. You simply remove the provided cover plate, install the optic using the included screws, and torque to 15 inch-pounds. It is not natively compatible with the larger Holosun 507C; that would require a different mounting plate.
Does it fit Glock 19 holsters?: No, it does not reliably fit Glock 19 holsters due to different slide and frame dimensions. You will need a holster specifically molded for the FN 509 series. We recommend checking with Vedder Holsters or Tier 1 Concealed, both of whom offer dedicated FN 509M models with lead times of 7-10 business days.
How long does shipping to an FFL take?: For in-stock items, processing and shipping typically takes 1-2 business days. Transit time varies by carrier and destination, but continental US deliveries usually arrive at your selected FFL within 3-7 business days after shipment. You must contact your FFL to coordinate transfer paperwork upon shipment notification.
Can I return it if I don't like the trigger?: No, firearms cannot be returned due to personal preference in trigger feel or other performance characteristics once the transfer is completed. All sales are final after the firearm is transferred to you at the FFL. We recommend handling one at a local range or retailer, or investing in an aftermarket Apex Tactical trigger kit for approximately $150 if you seek a different pull weight.

Sources & methodology. Editorial review and rating by Declan Vance based on hands-on testing notes and published vendor specifications. Pricing verified at time of publication. Last fact-checked 2026-05-29.