Field Test: FN 509 Midsize MRD

When perfection is the goal, good things happen. That’s the story with FN — a manufacturer committed to providing the U.S. military, local and federal law enforcement and the civilians of this great nation with quality firearms designed to perform. 

Having sent plenty of rounds downrange with FN firearms over the years, I was excited to give its latest addition to the uber-popular 509 Line a test drive. Dubbed the FN 509 Midsize MRD, this pistol arrived in an FN-branded soft case complete with a pair of 15-round magazines. Ten-round magazines can be selected upon purchase. In addition to the pair of magazines, the Midsize MRD also comes complete with the FN Optics Mounting System. This innovative system allows for the installation of many (10 commercially available optics) pistol-compatible optical sights as well as slide caps to cover the mounting surface should you decide to simply utilize the blacked-out iron sights. Other notable packaging includes two interchangeable backstraps, a locking device, and an owner’s manual. 

The FN 509 Midsize MRD comes with a FN-branded soft case along with a litany of other gear including the Optics Mounting System and a pair of either 10- or 15-round clips.

Like every FN I’ve ever triggered, the Midsize MRD showcased obvious craftsmanship — no dings or scratches — and a quick run-through showed exceptional functionality. The studded, ambidextrous magazine release buttons proved crisp, and magazines released with ease. New sculpting around the guard and the magazine release buttons make them easier to activate. The four-inch slide is smooth, and the ambidextrous slide stop engages and releases as advertised. A lighter weight yellow recoil spring has been added to make the slide easier to operate, and the shorter grip frame no doubt boosts concealability. The polymer grip features a high, perfectly recessed throat, which allows for a high-as-possible grip. The grip also showcases studded palm-swell, finger and thumb areas; all of which help ensure consistent hand placement. The MIL-STD-1913 accessory mounting rail located under the muzzle on the midsize frame allows for accessory attachment. I also gave an instant hat-tip to the Trigger Safety — a feature that blocks the rearward movement of the trigger unless the shooter’s finger is on the trigger. 

The Trigger Safety on the FN 509 Midsize MRD prevents the rearward movement of the trigger unless pressure is placed on the trigger by the shooter’s trigger finger.

An engineering masterpiece, the FN 509 Midsize MRD was built for performance and shot-to-shot repeatability. As for its aesthetics … the firearm is a work of art.

Let’s Shoot

I opted to stay with the standard iron sight system and my first mission was to cycle a pair of magazines through the Midsize MRD at a close 10-yard target. I wanted to get a feel for the pistol’s 26.5-ounce weight, recoil and the like. 

The front and rear cocking serrations make for rapid round chambering, and the pistol throws down on the target very well. Recoil in this 9mm pistol is virtually nonexistent, making it easy to get back on target and send another round accurately downrange. I give some credit here to the interchangeable backstraps. They really help with recoil management. The trigger boasts a flat-face, which cradles the index-finger and ensures a solid feel and repeatable squeeze. 

Recoil with the FN 509 Midsize MRD is virtually non-existent, making it possible to reacquire the target after each shot is executed. The flat-faced trigger is comfortable and was designed for safety and consistency.

The first 15 rounds were shot slowly, and the second 15 were cycled as fast as I could squeeze the trigger. The FN 509 Midsize MRD cycles like a dream — chalk this up to a built-by-hand and not-a-machine design. Plus, the FN 509 platform is the most tested FN pistol to date with more than 1 million rounds sent downrange. If there were glitches, FN engineers discovered and remedied them. The polished chamber and feed ramp also assist in picture-perfect cycling. Casings were ejected with vigor, flying high and landing over 20-feet to my right. Over the course of five days, I cycled 300 rounds through the FN 509 without a single field-strip cleaning and not once did I experience any jamming issues. The gun proved a joy to shoot and is as reliable as the day is long.


This pistol made me look like a lot better shot than I know I am. This is important. When it comes to home defense, few things are more critical than knowing you can put the bullet where you want it should the worst possible situation present itself. Engineered with a twist rate of 1:10 RH, my Federal 115-Grain FMJ RN Brass Case rounds stabilized extremely well. I want to note that these rounds were designed for practice shooting and aren’t the ideal choice for home defense. For the sake of testing, I used Sinclair’s Simple Twist Rate Measurement method, and the branded twist rate of 1:10 proved correct. 

At a distance of 15 yards, I put four out of five rounds in a 2-inch diameter Birchwood Casey orange dot. Moving back to 30 yards, my grouping fell off a little, but I was still able to place three out of five rounds in the orange dot. For a struggling marksman like me, that’s pretty dang satisfying. I also, just for fun, fired a number of 50-yard plus shots at dirt creek embankment. I was picking holes in the dirt and just having fun. The front and rear co-witness iron sights are fixed but proved accurate.

This pair of groups were fired quickly from the marked-on-photo distances. Even for a struggling marksman like me, the FN 509 Midsize MRD proved accurate.

My wife and 14-year-old son also spent time behind the trigger. Both could easily manipulate the slide, and both were pleased with the fact that the firearm didn’t beat them up. They were able to get familiar with the pistol quickly, and accuracy for both came easily.

My bride had zero trouble handling the FN 509 Midsize MRD, and was pleased with its light recoil and exceptional accuracy.


Impressed with the grip and functionality of the pistol from the get-go, I was eager to get it out in some weather. The pistol’s enhanced grip features no doubt prevent slippage, but I was also impressed with the pistol’s performance in the downpour. I cycled 50 rounds without issue, and because the frame is polymer construction, clean-up was a breeze. I will note that these were the last 50 rounds I cycled before cleaning the pistol. 


The pair of polymer base, low-friction magazines don’t require thumb cramps to reload but aren’t at all sloppy either. The spring boasts ideal tension, and I appreciated the fact that both 15-round magazines were branded with numbers (1-15) that indicate exactly how many rounds are in each magazine. 

The pair of 15-round magazines aren’t sloppy or difficult to load.


Over the course of my five-day testing period, the FN 509 Midsize was stored in a by-the-bed lockbox, inside my wife’s concealed-carry purse, and in a standard hip holster. The 7.4-inch long, 5.2-inch high and 1.35-inch wide pistol proved compact and easy to tote and store. Most pleasing, however, is the fact that you can bank on full-sized pistol performance in a midsize package.

The FN 509 Midsize MRD fit easily into a small conceal carry purse.

Field Stripping

After cycling 300 rounds through the FN 509 Midsize, I figured I owed it a good cleaning. Field Stripping the firearm takes only seconds. Not equipped with a threaded barrel, simply lock the slide and rotate the takedown lever 100-degrees clockwise. While holding the slide with one hand, release the slide from the slide stop and let it come forward slowly, keeping the rear of the slide and the rear of the frame aligned. With the muzzle pointed in a safe direction, press the trigger to release the striker. Now remove the slide. The recoil spring and barrel remove easily, and reassembly requires only guiding the slide and barrel assembly on the frame and pulling the slide to its rearmost position. Now rotate the takedown lever to its original position.

Disassembly and reassembly are a breeze. Also, note the lighter weight yellow recoil spring designed to assist with recoil management.

Good For Home Defense?

There is no question this midsize pistol is an ideal choice for home defense. Personally, I like the fact that my wife can handle the weapon easily, and because it’s highly accurate, put the rounds where she would need them. I also love the fact that the pistol conceals easily and is a dream to tote. If you’re in the market for an everyday carry firearm or one that remains ready on the home front, the FN 509 Midsize MRD is an ideal choice. 


FN engineers wanted customers to be able to customize or mix/match components between their FN 509 pistols. Some of these options include:

  • The slides and barrels are compatible across all frames.
  • There are magazine sleeves to accommodate larger capacity magazines in your Midsize.
  • The sight dovetails are standardized to a #8 front and rear, making them compatible with several aftermarket options.
  • FN worked with throngs of holster companies to make sure holsters are available for all FN 509 models, including the Midsize.
  • For the first time in FN history, there are aftermarket options for triggers, barrels and other components

When it comes to the Optics Mounting System, FN engineers developed a system of different plates that insert into the factory-cut slide that accepts the majority of MRD’s on the market, allowing for a low-profile mount and co-witness with the suppressor-height iron sights. In addition, the Optics Mounting System allows the user to mount all optics directly to the slide, thus eliminating an extra set of screws. These enhancements mean a more reliable system that does not require Loctite and has the option for a much lower optic for easier transition from iron sights, a smaller more concealable package and a more durable platform all while expanding optic mounting capability. 

While the similarities between the FN 509 Standard and the all-new FN 509 Midsize far outweigh their differences, customers will notice the same reliability, durability and accuracy in the FN 509 Midsize that they are accustomed to in the standard FN 509. 

What are you waiting for? Add to your FN 509 Line today.

Additional Photos 

For more information visit FN America website.

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  • CW September 9, 2019, 11:23 pm

    FNS 9C would be the better choice IMO. You can find them cheaper, and the slide rails on the lower reciever are longer. Put in an APEX trigger, and full size FNS 9 mag release with the money you save.

  • Firemanbob September 9, 2019, 8:23 pm

    Great review, overall a quality weapon. checked out the price which seems a little high considering the competition like the CZ p 10 series, just saying. these in depth reviews are much appreciated.

    • Scott December 23, 2019, 9:58 am

      I own both fns 9c and 509 midsize.Both are fully amby.Both triggers are crisp with good resets.Both handle recoil real well.Both are great shooters and I alternate carry with Muddy river tactical iwb holsters.Fnquality.Love both guns.

  • TropicLightning September 9, 2019, 6:51 pm

    Trigger safety!! No external safety!!!!!
    If I want a Glock then I’ll buy a Glock..
    Where can I get a Browning/FN Highpower???

  • johnnyraygun September 9, 2019, 11:05 am

    I like the pistol and nice review. More and more are building for red dots and that is nice to see. The weakness is the trigger pull to release the slide. My XDM has a lever to release the slide. so it is not hard to design that feature into what could be a great gun.

    • Patrick Roberts December 23, 2019, 5:55 am

      Trigger pull to release the slide? I assume you are talking about disassembly? I can’t say that is really a weakness, you have to lock the slide to the rear to rotate the takedown lever. I never understood why people feel that this is an issue.

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