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The FN 509 Midsize MRD is the sweet spot of the FN 509 family. You get a 4-inch cold hammer-forged stainless steel barrel with a recessed target crown and polished feed ramp on a grip that's trimmed down enough to carry daily without fighting it. At 26.5 ounces and 7.4 inches overall, it lands right in Glock 19 territory size-wise, but FN brings a different feel to the ergonomics. The tri-textured grip panels and interchangeable backstraps let you dial in the fit, and the grip angle sits neutral enough that new shooters get along with it quickly while experienced hands will feel right at home. This FDE version ships in 10-round configuration, making it the right pick for certain markets.
The FN Low Profile Optics Mounting System is genuinely one of the better factory solutions in this class. Rather than just cutting the slide and calling it a day, FN uses adapter plates paired with O-rings that apply constant upward pressure on the optic, helping prevent mounting screws from walking loose under recoil. The system supports direct mounting of more than 10 different miniature red dot sights, covering popular footprints from Trijicon, Holosun, Aimpoint, and others. The co-witness iron sights that come standard are already at suppressor height, so when you drop a red dot on, you have a usable backup sighting solution without buying anything else. That's a detail a lot of manufacturers skip.
FN put real thought into the controls on this pistol. Both the slide stop lever and magazine release are fully ambidextrous, so left-handed shooters aren't left working around the gun. The flat-faced trigger gives you a more consistent finger placement shot to shot and a cleaner break than the earlier hinged trigger design. The slide wears both front and rear serrations that actually bite, and the MIL-STD-1913 accessory rail under the dust cover keeps your options open for lights and lasers. Reliability across the 509 platform is well documented, with the platform having been tested well beyond one million rounds and adopted by agencies including the LAPD for duty use. For the range, for carry, or for home defense, this is a pistol that doesn't need much apology.
The FN Low Profile Optics Mounting System supports direct mounting of over 10 different miniature red dot sights through included adapter plates. Popular compatible footprints include the Trijicon RMR and SRO, Holosun 407C and 507C series, and the Aimpoint Acro, among others. For micro-footprint optics like the Holosun 507K, you'll need a separate third-party adapter plate since that footprint isn't covered by the factory-included plates. It's worth double-checking compatibility with your specific optic before purchasing.
Yes. This 10-round version is compatible with larger-capacity FN 509 magazines, including 15-round and higher-capacity options, when used with a grip sleeve adapter. FN 509 magazines are interchangeable across the Midsize MRD platform, giving you flexibility to run different capacity options depending on your needs.
No, this model does not have a manual thumb safety. The only built-in safety mechanism is the trigger safety integrated into the flat-faced trigger. This is consistent with the majority of modern duty-grade striker-fired pistols and is the preferred setup for many carry and duty applications.
The two are very close in overall dimensions. The FN 509 Midsize MRD has a 7.4-inch overall length and 5.2-inch height, putting it in the same general class as the Glock 19. The grip angle on the FN 509 is more neutral than the Glock, which many people find easier to point naturally, especially those transitioning from other platforms.
Yes, the two included backstraps swap out quickly without tools. The difference between the flat and arched backstraps is noticeable in hand, and choosing the right one can meaningfully affect your grip comfort and trigger reach. FN also offers a larger backstrap separately for those who need a bit more palm swell.
The 509M MRD ships with suppressor-height iron sights that are specifically sized to co-witness through the window of most miniature red dot sights. This means once you mount a compatible optic, you still have a functioning iron sight backup without buying or installing anything additional. It's a practical feature that adds real value, especially for anyone using this pistol in a defensive or duty role.
| UPC | 845737011574 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | 66-100742 |
| Action | |
| ATF Type | Pistol |
| Barrel Length | 4" |
| Caliber/Gauge | 9mm |
| Capacity | 10 + 1 |
| Color | Flat Dark Earth |
| Length | 11.5 |
| Number of Magazines | 2 10 rd. |
| Package Height | 2.5 |
| Package Width | 8.2 |
| Product Type | Semi-Auto Pistol |
| Safety | No |
| Shipping Weight | 3.3 |
| Sights | Black Co-Witness Iron Sights |
| Sights Type | Co-Witness Iron |
| Slide Description | Optic Ready/Serrated |
| Units per Box | 1 |
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