FN 509 Midsize MRD Review: I Really Shot It This Time – Review

The FN 509 Midsize MRD has been a great carry pistol over the last several months. If you are looking for a new pistol, this may be the most versatile option on the market right now.

U.S.A. –-(Ammoland.com)- If you recall my last article on the FN 509 Midsize MRD, you might recall that I wrote a “review” of the gun even though I never even shot it. Since reviewing a pistol that I had never shot was a bit unconventional, I also agreed to review the Midsize MRD in a more traditional manner once I had enough time with the new pistol. If you are curious, I highly recommend reading the “no shots fired review” I posted a few months back.

Now I should tell you upfront, I have been a huge fan of the FN 509 platform since my first exposure to it back in 2016. While generally underappreciated, the platform offers some things that I personally prefer in a pistol. Obviously we will dive into those features with more detail but the major points are outstanding slide serrations, a solid grip texture, and the best OEM MRDS mount on the market.

The FN 509 Midsize MRD’s Features

The FN 509 Midsize MRD carries over all of the same features you find on the 509 Midsize but adds the FN Low Profile Optics Mounting System from the 509 Tactical.

If you missed our review of the FN 509 Midsize, there were several small enhancements made to the frame based on feedback from consumers and industry experts. You might notice that the mag release is easier to use thanks to the reshaped fencing around the button and that the Vickers style slide release from the Tactical was carried over to every model introduced afterward.

The reshaped mag release fence that was rolled out with the Midsize is used on the Midsize MRD.

Also new for the 509 Midsize frames was a larger textured area on the rear of the grip to improve purchase on the gun resulting in a much nicer feel in the hand. Sometimes the smallest change can make a huge difference.

Expanded texturing on the back of the grip means more control over the pistol.

Speaking of small changes that make a difference, the factory trigger has a much flatter face to it in an effort to promote a straight to the rear trigger pull. My example’s trigger measured out at 6 pounds even after the 1,600 or so rounds I put downrange with the stock trigger. For the last 400 – 500 rounds I installed an Apex Tactical curved trigger which dropped the weight of the trigger to 5 pounds 4 ounces.

The flatter trigger used on the Midsize is obvious when compared to the earlier trigger.

FN also saw fit to offer magazine spacers for the 17-round and 24-round 509 Tactical mags should you decide to carry a magazine larger than the flush-fitting 15-round mag the 509 Midsize ships with. Like with all pistols, ensuring the mag can’t be over inserted is crucial to preventing damage to your firearm so make sure you use the proper magazine sleeve.

If you use the appropriate over-insertion spacer, you have the option to use 17 or 24-round magazines in addition to the flush-fitting 15-rounder.

If you have joined the 21st century, you will be pleased to see that FN used their outstanding FN Low Profile Optics Mounting System paired with black suppressor height irons. FN also used a new MRDS cover plate that lacks the protective wings you find on the 509 Tactical.


  • Caliber: 9mm
  • Action Type: Striker Fired (technically DAO)
  • Controls: Ambidextrous Slide Stop and Magazine Release
  • Frame: Polymer With Replaceable Steel Slide Rails
  • Magazine Capacity: 10, 15, 17, or 24 Rounds (17 and 24 round mags must use over-insertion spacers)
  • Weight Unloaded: 26.5 Ounces
  • Barrel: 4″ Stainless Steel Cold Hammer-Forged
  • Length: 7.4″
  • Height Without Optic: 5.2″
  • Width Including Slide Stop: 1.35″
  • Trigger Weight As Tested: 6-Pounds
  • Sights: Black Front & Rear Co-Witnessing Suppressor Height
  • MRDS Mount: FN Low Profile Optics Mounting System
  • Included Accessories: Two Backstraps, Two Magazines, MRDS Cover Plate, Zippered Case, MRDS Mounting Kit

Why The FN 509 Midsize MRD Is The Best Pistol Value For Sale Today

There is a ton to like about the FN 509 platform and several reasons that I think the 509 Midsize MRD is the most relevant model they have released to date.

There isn’t another pistol on the market that offers a better multi red dot mount from the factory. I touched on this in the “no rounds fired review” published a couple of months ago, but once you start looking at other pistols currently for sale the FN 509 Midsize MRD starts to edge out the competition.

FN used the same fantastic MRDS mount that was introduced with the 509 Tactical.

Without getting too technical, the FN Low Profile Optics Mounting System has continued to impress me. I have a ton of time behind both the FN 509 Midsize MRD as well as the FN 509 Tactical, both share the same mounting system. With roughly 14,000 rounds downrange on an FN Low Profile Optics Mounting System equipped slide, 2,000 of those being the FN 509 Midsize MRD, I have never once had an optic come loose or lose zero. An impressive feat when you consider the FN mounting system uses no thread locker by design where competing systems often struggle even with thread locking compound.

Hell, the mounting system is so good that Aaron Cowan of Sage Dynamics considers “the best designed and supported OEM optics platform currently offered.” That is some lofty praise, especially from a dude that breaks more stuff than anyone I know.

When you compare a Glock 19 to the FN 509 Midsize MRD, they are nearly the same size.

In the “No Rounds Non-Review” I broke down the next nearest competitor, the Glock 19 Gen 5 MOS, and outfitted them to be on the same level of performance. The FN 509 Midsize MRD came in at $1,113.98 when you add a Holosun HS407C, Henry Holster’s Spark, Discrete Carry Concepts Mod 4 Universal belt clips, Streamlight TLR-7, and an additional mag to bring the total to three like the Glock.

The Glock 19 MOS Gen 5 came in at $1,171.96, nearly $60 more than the FN 509 Midsize MRD. When adding everything up for the Glock to be carry ready like the FN 509, I was forced to add in some parts that I didn’t have to on the FN to place them on the same playing field like the Vickers mag release and the Kagwerks slide release. Even with the extra parts left out, the Glock was still within $10 of the FN 509 and I don’t feel like that is enough savings to overlook the problematic MOS mounting system.

The FN 509 Series Isn’t Perfect

Now just because I have a laundry list of likes about the FN 509 platform, there is some stuff that I really wish that FN would address. Keep in mind just like the aspects of the 509 that I like, the things I don’t like are very personal and will vary from shooter to shooter. As much as I would love to keep reviews objective, that isn’t realistic. Overviews are objective, a review is built on the observations of the author.

That said, I want to reiterate that the following “cons” are 100% my opinion after 3 years with the FN 509 platform and more than 18,000 rounds.

The left 509 frame is as the pistol ships, on the right you see the 509 Midsize frame that I removed some material from in an effort to eliminate the hotspot created by the blocky beavertail.

Even though the FN 509’s ergonomics are among the best you can find in a stock pistol there are a couple of aspects of the grip that I feel could be improved. The beavertail area of the grip is a bit on the blocky side for my grip style. I addressed this on my own 509 Midsize MRD by sanding the left side of the beavertail a touch to round the surface out a bit which improved the pistol’s feel tremendously.

Keep in mind that this isn’t something everyone would even notice, it is purely a personal preference thing. In fact, it is so prevalent on just about every pistol that I have developed a pretty thick callus on my thumb.

The Midsize has far more grip on the backstrap than the original 509 or Tactical grip.

The other area of the grip that I felt needed some love on the full-size grip has been addressed with the Midsize frame, the backstrap. The original backstraps for the full-size grips only had a narrow strip of texturing, thankfully the Midsize frame wrapped this texturing around the sides of the backstrap and greatly improved the grip.

There are a couple of options to address the full-size gun’s backstrap, one from Agency Arms who also offers a comp made specifically for the FN 509.


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Volker Precision also offers a more aggressive backstrap should you want one. I haven’t personally tried either one so I can’t tell you how much of an improvement over the original they are.


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The one aspect of the FN 509 series that I feel can absolutely be addressed is the magazine pricing. Somehow I feel as though the $49 MSRP for the standard 15 or 17-round mags and $60 MSRP for the 24-rounders is a touch on the excessive side. If CZ-USA can offer P10 C magazines for $35 MSRP, I am not entirely sure why FN America can’t be slightly more competitive with the mag pricing, especially when the perception of what a magazine should cost has been skewed by sub $20 Glock magazines for years.

CZ P10 C magazine on the left, the right is an FN 509 Midsize magazine.

How Is The Aftermarket For The FN 509?

Since I have been spoiled by the expansive Glock aftermarket like many other shooters, that is always something I take into consideration when reviewing a platform. As always, I prefer to shorten the trigger reach as much as possible with a flat-faced trigger. I went with a flat face Apex Tactical unit just like the one I wrote a 2,000 round review on a while back since the upcoming Volker Precision trigger wasn’t quite ready.

Just the other day I got confirmation that the Apex Tactical curved FN 509 trigger and the Volker Precision trigger are on their way to my mailbox, which should make for a nice comparison article. Who doesn’t like a product shootout?

The new curved Apex Tactical 509 trigger in the rear, in front is the new Volker Precision 509 trigger.

The FN 509 has seen some support, but not quite as much as I would like to see. The number of companies stepping up to the plate with a litany of aftermarket parts built for the FN 509 platform should tell you that the pistol has captured the attention of those in the firearms industry. You can find aftermarket strikers, barrels, model-specific compensators, and even magwells if that is your thing. (Magwell note: Unfortunately there isn’t a magwell that I feel is a great option yet, hopefully, someone comes up with a good design soon.)

Apex does make a great aftermarket threaded barrel if you would like to run a compensator or suppressor on your Midsize MRD. You can read my 2,500 round review of that barrel on my own blog, Firearm Rack.

I can’t recall the last time a new platform got this much support without several large agencies adopting a gun. There is a good reason that the 509 hasn’t won many agency contracts, the lack of good retention holsters up until very recently when Safariland finally added the FN 509 to their line. Sadly there isn’t an option for an MRDS equipped 509 in the Safariland fitment guide yet.

Carrying the FN 509 Midsize MRD

While the FN 509 Midsize MRD hasn’t entirely replaced my Glock 19 carry guns, it does get carried far more than I expected it to. Since my normal carry pieces are wither compensated or ported, the Midsize MRD fills the gap I created for a Glock 19 sized gun without some form of compensation.

Since Andrew of Henry Holsters offers the Spark holster for the FN 509 fitted with the TLR 7, choosing a holster was an easy task. Why the Spark? There are a few things I look for when choosing a holster, compatibility with overhooks so I can fit Discrete Carry Concepts clips, some form of wing/claw, and some form of wedge on the back.

My FN 509 Midsize MRD in the Henry Holsters Spark AIWB holster. It has been fitted with Discreet Carry Concepts Mod4 universal clips for a lower profile package.

While the wing/claw and wedge are pretty self-explanatory, you might be curious as to why I fit the DCC clips to my holsters. Simply put, the DCC clips are lower profile, are far more secure than plastic clips, and provide more stability when paired with my Ares Gear Aegis belt.

I also carry a reload in a modified Bawidimann Uber Vertical mag carrier for Glock mags not because I think there is a possibility of a drawn-out gunfight, but as insurance in the unlikely event that a malfunction occurs. If I am going carry a spare, it might as well be the 24-rounder since getting that into the gun is not only easier but it also gives you more bullets should whatever unfortunate situation you find yourself in calls for that.


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Shooting the FN 509 Midsize MRD

As of the time that I am writing this review, I have north of 18,000 rounds through the FN 509 platform in one iteration or another. The bulk of that was through my FN 509 Tactical, but since the pistols are so similar in many ways what I learn on the Tactical often translates to the Standard, Midsize, and now the Midsize MRD.

I have never found the FN 509 series to be lacking in the accuracy department, the 509 Midsize MRD was no different. one of the most impressive groups that I shot with the 509 Midzise MRD was the 1.28″ 10-yard, 10-shot group.

The FN 509 Midsize produced an impressive 1.28″ 10-shot group at the 10-yard line. If the best 9 are measured, the group shrinks to only 0.47″.

Defensive ammo was a bit snappier than the original FN 509 due to the use of the reduced power recoil spring but not unmanageable. I did replace the recoil spring assembly with the stouter silver spring leftover from my Tactical when carrying it with the Federal HST 124-grain +p since I wasn’t using it in my Tactical. The result of the change was a slightly flatter shooting gun when shooting super hot defensive loads.

With my preferred carry load, Federal HST 124-grain +p, the FN 509 Midsize MRD put 10 shots into a 1.39″ group from 10-yards.

I was rather impressed with the 509 Midsize MRD’s capabilities at 25-yards using run of the mill S&B 124-grain FMJ. A 2.18″ 10-shot group isn’t anything to scoff at when shooting range ammunition. Hell, that is an impressive group even if shooting match or premium defensive ammo.

Seller & Bellot’s 124-grain FMJ also performed well with a 2.18″ 10-shot group at 25-yards.

At 25-yards the 509 Midsize MRD produced a sub 2″ 10-shot group with my defensive loads, something not possible with many off the shelf guns. Generally, I would be pleased with a 3 to 4″ group out of most pistols but I am always happy with better results. Since I was running low on HST, I managed to get a 10-shot group in before using the remaining ammo to finish zeroing.

Again, my Federal HST 124-grain +p carry load performed well producing a 1.93″ 10-shot group at 25-yards.

You might be wondering about the pistol’s reliability. With a couple of thousand rounds through my Midsize MRD, I never saw a malfunction. In fact, I have only had a single malfunction in the 18,000 or so rounds I have through the FN 509 platform that wasn’t induced by the failure of an aftermarket part I was testing.


Like every other FN 509 iteration I have reviewed since the launch of the line, the Midsize MRD is a fantastic pistol. Not only is it a great concealed carry pistol, but it is fantastic on the range as well.

There are some small things that I addressed to tailor the pistol to my personal preferences such as trimming the backstrap to function as a sort of bobtail, removing a bit of material in the beavertail area, and adding an Apex Tactical curved trigger. That isn’t to say that the pistol isn’t outstanding out of the box, but my nature as a tinkerer takes over sometimes.

That said, I have no issue recommending the FN 509 Midsize MRD in just about any role it might be used in. The Midsize MRD is small enough to be concealed easily with a good holster while remaining large enough to give you a good experience on the range. Sure, something smaller might be easier to conceal, but oftentimes that results in a pistol that the owner is less likely to practice with.

I did make a small alteration to the backstrap in order to make the Midsize MRD less likely to print. After removing the small portion of the grip, I didn’t feel like the pistol was harder to grip.


  • The perfect size for concealed carry and recreational shooting
  • Fully ambidextrous
  • Outstanding ergonomics
  • Solid aftermarket
  • One of the most accurate polymer pistols I have tested out of the box
  • Uses the best factory multi-model MRDS mount ever offered


  • Magazine prices are a bit high
  • The trigger may be offputting to some (I found it to be acceptable though)
  • Fewer holster choices than I would like to see but that will grow as the pistol is adopted by more people

With an MSRP of $799, the Midsize MRD can be found for under $650 if you shop around. There is simply nothing that can touch it in terms of performance in the same price bracket.

You can find more information about the FN 509 Midsize MRD on the FN website.

About Patrick R.Patrick Roberts

Patrick is a firearms enthusiast that values the quest for not only the best possible gear setup but also pragmatic ways to improve his shooting skills across a wide range of disciplines. He values truthful, honest information above all else and had committed to cutting through marketing fluff to deliver the truth. You can find the rest of his work on FirearmRack.com as well as on the YouTube channel Firearm Rack or Instagram at @thepatrickroberts.

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American Patriot

Doesn’t look like a bad set-up but the grip texture looks awfully uncomfortable. I just bought a new VP9 & that looks & feels great in the hand (haven’t shot it yet due to weather) and the trigger is tremendous. I’m still carrying my G19 for now util I get a few hundred rds down range with the VP9, but even my Glock trigger is a hair over 4 lbs & at 6 for the FN to me that’s a big difference.