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FN 509 Series Review: Due Diligence

In 2011, the U.S. Army and U.S. Air Force announced they’d be undertaking a program to replace the military’s aging fleet of service pistols. In addition to the need to retire guns that had reached the end of their mechanical service life, handguns were seeing increased use by both special operations and conventional forces in an age of asymmetric warfare that required more direct-engagement by military personnel with local populations. This increased battlefield presence, combined with rapid commercial advancements in pistol capability, led the Defense Department to pursue what would eventually become the Modular Handgun System. Many competed, and more were interested in what would come from Fabrique Nationale: The FN 509.

The requirements were comprehensive. The pistol had to be capable of 90-percent accuracy inside a 4-inch circle out to 50 meters. No caliber was specified for final selection, but all submitted prototypes would undergo a terminal ballistics test and be expected to achieve 14 inches of penetration into a block of ballistic gelatin. Other requirements included fully ambidextrous controls, the ability to accept “targeting enhancers” (lights and lasers) on a Picatinny rail, and a matte finish in a neutral color. The military was also interested in enhanced ergonomic features that could accommodate a wide variety of hand sizes.

fn 509 review

It was against this backdrop that FN began working on the pistol that we know today as the FN 509. They started with their striker-fired FNS Compact and the requirements put forth by the DOD and set to refining and testing, to the tune of over 1 million rounds fired — with most of those being +P and military-grade rounds loaded to higher pressures and velocities than the majority of commercial ammunition. Those tests included drop-tests on concrete, dust-laden reliability, high- and low-temperature operating thresholds, and salt-spray corrosion resistance. In addition to these tests, FN implemented their own battery of proprietary performance tests that the 509 met or exceeded handily. What resulted was a series of overhauls of the FNS base platform that included changes to the slide, barrel, and frame, in addition to a complete redesign of other components to enhance reliability and function.

fn 509 tactical

The fiberglass-reinforced-polymer frame was reshaped and contoured to fit almost every possible combination of hand size and shape out there. Specifically, they targeted the 5th to 95th percentiles of hand sizes for both men and women, in accordance with MHS program requirements. Grip texture was enhanced and optimized for hard use under all conditions. To achieve this, the FN 509 actually uses three separate texture patterns: a pyramid-like block structure on the sides, a scalloped “dragon scale” style on the front and backstraps, and a finer skid tape texture on the high edges. Additionally, molded guards “fence in” the controls in order to minimize the possibility of accidental activation of the slide-lock lever or magazine-release button. The slide serrations were also enhanced with more aggressive texturing. All of this was to achieve maximum ergonomics and tactile feedback to the user’s hand regardless of hot, cold, wet, or slippery conditions, or while wearing duty gloves. All commercially available 509 models also ship with two separate backstraps — a curved medium and straight-back small. These are easily replaced by the end user by simply tapping out a roll pin and sliding off one backstrap, then sliding the new one on and replacing the pin.

The stainless steel barrel was also redesigned with an 11-degree recessed target crown, and the barrel itself is cold-hammer-forged in the tradition of FN’s other military-grade offerings. They moved away from commercial PVD finishes and use ferritic nitrocarburation (also known as “nitride”) finish on these barrels. This process actually alters the surface of the barrel material on its surface layers, as opposed to being an applied finish, offering greater wear resistance over long-term use.

509 compact review


While the Modular Handgun System solicitation was trudging along, FN wasn’t content to rest on their laurels. Between their submission to the MHS trials in 2016 and the FN 509’s commercial release, they took their redesigned fighting pistol and approached a number of law enforcement agencies around the country with test guns to collect real-time feedback from officers, leading directly to the enhanced magazine release, slide and barrel changes, as well as some size and shape input to optimize it for duty holsters. A number of LE agencies have since adopted the pistol as their issued duty sidearm. Additionally, U.S.-based corporate security company Brinks adopted the pistol for all of its armed security professionals.

In 2017, FN released the 509 to the commercial market and have been advancing the design ever since. To date, there are four separate models available: the original 509, the 509 Midsize, the 509 Compact MRD, and the 509 Compact Tactical.


One of the biggest advancements in self-defense and duty pistols over the last decade-plus is the revolution in miniaturized red-dot optics. Once thought the strict purview of competition shooters and “gamer guns,” red dots are now considered all-but-standard on well-appointed pistols meant for offensive and defensive tactical applications. Traditionally, mounting a red dot to your pistol’s slide required milling the slide itself for a specific optic, necessitating the time and effort of a professional machine shop and all the costs that entailed. Plus, it was a permanent modification to your pistol’s slide that would only accommodate a single brand or type of optic. Then came mounting plates, whereby your optic was mounted to an interface plate that was then mounted to the slide. This allowed the use of multiple types of optics by changing the interface plate, which is the system FN was using a decade ago — long before many of their competitors — on the FNP-45 pistol.

fn 509 plate review

But engineers at FN found this setup introduced failure points into the optic/pistol system. So when the time came to release the FN 509 Tactical, and the subsequent MRD (Miniature Red Dot) models, they overhauled their mounting method to a three-part system consisting of a plate, optic-specific mounting lug, and the slide itself. This system allows the user to use a much wider array of optics — the list currently sits at 17 different types of optics from various brands and is ever-expanding. New-production Tactical and MRD models ship with a prepackaged set of plates and lugs, so that the consumer doesn’t have to purchase a new plate/lug setup if they wish to change optics throughout the life of their pistol. Tactical models also ship with suppressor-height night sights, a threaded barrel, and two different recoil spring units to optimize use with a suppressor.

fn 509 magazines


The FN 509 was designed from the outset to be a pistol platform. As such, the slides and frames from the various models are all interchangeable. Want to put a Compact MRD slide on a full-size FN 509? No problem. Want to put the 509 Tactical slide on the 509 Midsize? Also, no problem. The only issue you’ll run into is that the Compact slides will leave a small gap between the muzzle and the end of the frame when mounted to larger-size frames. However, if you were to use the Compact Tactical slide on a larger frame, the threaded barrel will allow you to run a compensator, which will nest itself into that gap for a clean, integrated look. Same, by the way, goes for their magazine. Any higher-capacity magazine will fit in any smaller frame. FN 509 magazines are available in 12-, 15-, 17-, and 24-round sticks. While the 12-rounders will only fit in the Compact MRD and Compact Tactical models, you can always put a larger mag in a smaller gun. While a 15-round mag from the 509M will not fit in the larger 509 Tactical, it will fit in both Compact models. The 17- and 24-round magazines from the FN 509 and 509 Tactical will fit into any other 509 variant. There is also a whole line of grip sleeves available from Midwest Gunworks or direct through FN’s e-store. There is a wide variety of sleeves available to create a seamless grip between any magazine size and any frame size.Speaking of compensators and other things, FN has made a point to open the FN 509 up to aftermarket support, so parts and accessories like triggers and comps are already available to mount and install in the event you want to seek further refinement of your personally owned 509. (Editor’s note: It should be noted that the installation of aftermarket parts could potentially cause damage to your pistol and void your warranty.)

For anyone looking to get themselves into a high-quality, hard-use, modular pistol with stake-your-life-on-it reliability at a competitive price point, the FN 509 provides a turn-key answer for everything from concealed carry to duty use, and it’s been tested to rigorous standards from a company well-known for producing some of the world’s most battle-proven firearms.

franken 509

Franken Five-09

To test the plug-and-play capability of the 509 as a whole platform, we built our own “ideal” 509 pistol, cobbled together from as many different variants as we could include plus some aftermarket parts. The pistol pictured here is what we came up with. It consists of the following:

+ 509 Midsize frame

+ 509 Compact MRD slide and recoil spring assembly

+ 509 Compact Tactical threaded barrel

We then upgraded the internals with Apex Tactical’s Action Enhancement Kit and heavy-duty striker. Using the compact slide on the midsize frame left a small gap between the muzzle and the end of the frame. This was ideal for attaching the Parker Mountain dual-port comp, which sits recessed into that frame gap for a reduced overall length as well as nice, clean aesthetics. Finally, we took advantage of the MRD mounting system to add a Holosun 507c and a SureFire X300V light.

Editor's Note:Photography by Niccole Elizabeth and Tamara Keel.

This article and More appeared in RECOIL #50.

More on the FN-509

  • At NRA 2019, we stopped by Fabrique Nationale to check out the FN509, Here's the Video.
  • The FN 509 Compact: Any Red Dot, Any Light: a Leg-Up in the Micro Handgun Arena. Read More.
  • Taking the high-road: The FN Mid-Size. Here's the Announcement.
  • The FN 509 Tactical wins Handgun of the Year from NASGW-POMA. Read More.
  • Does the FN 509 make the Cut for best 9mm Pistol? Here's the List.
  • Apex Tactical makes more than just triggers for the FN 509: barrels and failure-resistant extractors. Read More.
  • Optimized for competition, the FN 509 LS Edge takes the striker fired handgun to the races.

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One response to “FN 509 Series Review: Due Diligence”

  1. some guy says:

    could you put the mid-size slide on the compact frame?

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