Apex FN 509 Threaded Barrel Review: 2,500 Rounds Later

Disclaimer: The Apex FN 509 Threaded Barrel was provided at no charge for this review.

It isn’t a secret that I have been a fan of the FN 509 platform since it was revealed to me at a media event during SHOT 2016. As you might expect, I have kept close tabs on what accessories are being produced for the pistol, so when I heard that the Apex FN 509 threaded barrel prototype was finalized, you can bet that I wanted to get my hands on it.

Apex FN 509 Threaded Barrel
A Prototype Apex barrel next to the production model.

Originally the prototype barrel that Apex Tactical gave us was intended for an ill-fated SHOT Show gun build that involved the FN 509 Midsize. Sadly, that project didn’t come to fruition due to several factors such as our preferred machine shop, ATEi, being on vacation during the build window and our second line choice being one of the worst communicators we have ever tried to work with.

But, making lemonade out of lemons, we were able to get a ton of time on the range with the prototype barrel and were able to get our hands on one of the very first production barrels as well.

Apex fn 509 barrel compared to factory barrel
Top: A New apex FN 509 Threaded Barrel; Middle: The Apex prototype barrel after roughly 500 rounds; Bottom: A Factory FN 509 Tactical Barrel after more than 6,000 rounds.

What does that mean? It means that I have in excess of 3,000 rounds through both the prototype and the production barrels. Over 2,500 of those rounds fired were through the production barrel suppressed, compensated and bare muzzle.

Not only does that mean good data to form an opinion with, but it also means that we shot the average amount of rounds one of these barrels will see in the average buyer’s barrel over roughly a 5 year period.

Before you start questioning the round count because of how clean the production barrel is in the photos, know that they were taken immediately after getting the barrel in the mail.

First Take Of The Apex FN 509 Threaded Barrel

The machine work on the Apex barrel is absolutely on par with the factory threaded barrel. Personally, I could have done without the fluting on the barrel if given a choice, but I guess it adds value for some people. The black Melonite finish appeared to be of high quality and I suspect that it will resist wear quite well.

Dropping the barrel into my FN 509 Tactical slide as well as the FN 509 Midsize, I found that the barrel fell right into place without the need for fitting. The lockup of the barrel to slide felt very close to the OEM barrel when I pressed down on the locking hood, no concerns there.

The Apex FN 509 Threaded Barrel: Same Same, But Different

The dimensions and fitment of the Apex FN 509 threaded barrel are largely identical to the OEM threaded barrel, but there are some key differences.

Where The Apex Barrel Is Identical To The OEM Barrel

Both barrels have a 1:10 twist rate, they both share the same dimensions in critical areas as best I can tell, the thread profile is identical, and the lockup feels to be identical. Functionally, I don’t believe that the Apex barrel too far off from the OEM 509 threaded barrel based on my range time. I can’t say that for certain without better tools to measure things like bore diameter, erosion, and a crap ton more rounds down range in lab-like conditions.

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Where The Apex Barrel Is Different To The OEM Barrel

There are some differences between the Apex FN 509 barrel and the OEM barrel, but none of them affect the performance of the barrel when compared to the stock unit as best I can tell. You do get some fluting that sets the Apex barrel apart from the OEM barrel but adds nothing beyond some cosmetic appeal if you are into that kind of thing.

FN 509 Comp
The Apex FN 509 threaded barrel has some flutes machined into it. The barrel worked well with the Henry Holster 4-port comp for the 509.

The feed ramp is slightly narrower than the OEM barrel, which I didn’t feel as though changed the performance of the barrel. While I didn’t see it cause an issue, I am not a firearm engineer and there may well be a reason the OEM barrel has a wider feedramp. There are some other dimensional differences in non-critical areas that don’t impact the performance of the barrel in front of the locking block and in front of the locking lugs.

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The largest annoyance about the Apex FN 509 threaded barrel is the thread protector. Personally, I prefer the more traditional knurling on the OEM thread protector both aesthetically and functionally. It seems as though the Apex thread protector offers less grip when I had oil, dirt, or liquid on my fingers. There was more than one occasion that I had a hard time getting it off when cleaning the pistol.

FN 509 Thread Protector
The slanted knurling offers less grip than the FN 509 Tactical thread protector.

In addition to the slightly disappointing knurling, the Apex 509 thread protector doesn’t incorporate the o-ring into it like the OEM thread protector. When mounting a suppressor you need to remove the o-ring altogether making you keep track of the thread protector AND the o-ring.

apex 509 threaded barrel
While the thread profile is identical, the o-ring is not captive in the thread protector.

Is The Apex FN 509 Threaded Barrel Accurate?

Before I get into how accurate the barrel was or wasn’t, I should state upfront that every group I shot with the Apex threaded barrel was offhand, without a rest. If I am going to shoot, I am going to get some skill-building out of it. At no point during my time on the range with the Apex 509 barrel did I notice a degradation in group sizes when compared to the factory barrel. I also didn’t see an increase either.


Ammo Brand & Weight Group Size POI Adjusted B8 Score
American Eagle 147-grain FMJ 0.901″ 100/100 – 10X
7-yard group with apex 509 barrel
The Apex 509 barrel produced an impressive 0.901″ group at 7-yards.


Ammo Brand & Weight Group Size POI Adjusted B8 Score
Blazer Brass 115-grain FMJ 1.725″ 100/100 – 10X
Federal HST 124-Grain +P JHP 1.756″ 100/100 – 9X
Sellier & Bellot 124-Grain FMJ 1.976″ 100/100 – 8X
Federal HST 147-Grain JHP 2.135″ 100/100 8X

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Ammo Brand & Weight Group Size POI Adjusted B8 Score
Federal HST 124-grain +P JHP 2.811″ 99/100 – 8X
Federal HST 147-Grain JHP 4.395″ 95/100 4X
American Eagle 147-grain FMJ 4.429″ 98/100 – 5X
Sellier & Bellot 124-Grain FMJ 5.083″ 95/100
Winchester White Box 115-Grain FMJ 5.943″ 92/100 3X

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Is The Apex FN 509 Barrel Reliable?

Short answer: Yes.

With 2,500 rounds fired through the Apex FN 509 threaded barrel, I can say that I didn’t experience any reliability issues. When I installed the barrel, I made sure to give it a light coat of oil and cleaned my pistol at the same time. With everything all slicked up, running the slide felt just like it has for some time now with the stock barrel installed.

The barrel didn’t get a cleaning until after 1,500 rounds or so, and when it was cleaned it only got an OTIS Ripcord bore snake pulled through it, a wipe down to remove excess carbon, and then some fresh oil before it was pressed back into service.

I shot the FN 509 with a SilencerCo Octane 45 HD, the Henry Holsters 509 comp, and with no muzzle device. In every instance, it performed on par with the OEM FN 509 barrel. In short, the thing is boringly reliable.

How Does The Apex Barrel Hold Up?

When inspecting the barrel for wear and any peening, I found no signs other than some metal deformation in the same place that the OEM FN 509 barrels have. It isn’t abnormal and stops deforming once it reaches a certain point in my experience.

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While I am not an engineer, I will wager an educated guess that that area sees far more pressure against the locking block during the unlocking process than other parts of the barrel. Again, this is 100% normal and you shouldn’t be concerned about it.

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What about finish wear? The Melonite finish holds up quite well and I am very pleased with the finish wear. I would say that it isn’t quite as resistant as the factory finish, but isn’t near as bad as I saw on the Faxon Glock barrel I reviewed for Ammoland a while back.

Do I Recommend The Apex FN 509 Threaded Barrel?

If you already have a threaded barrel in your FN 509, I can’t think of a reason that I would recommend the Apex FN 509 Threaded Barrel.

Now if you like the look of a fluted barrel or need a threaded barrel for your FN 509 Midsize or 509 Standard, the Apex FN 509 Threaded barrel is the best option for you, especially since you can’t buy a factory FN 509 threaded barrel currently.

The best part about the Apex 509 barrel is you can get a yellow reduced power spring without buying a gun.

The recoil spring is a factory FN 509 yellow spring.

You can find more information about the Apex FN 509 threaded barrel on the Apex Tactical website. The barrel carries an MSRP of $219.95 but can be found for around $200 if you shop around or use a Brownells coupon code.

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About Patrick Roberts 217 Articles
Since founding Firearm Rack in 2014 which evolved into Primer Peak in 2020, Patrick has been published by RECOIL, Ammoland, Gun Digest, The Firearm Blog, The Truth About Guns, Breach Bang Clear, Brownells, The Shooter's Log, and All Outdoor. When he isn't writing you can find him instructing handgun and AR-15 courses, training his dog Bear, or spending time with his son Liam. See what he is up to on his YouTube Channel, on Facebook, or on Instagram at @thepatrickroberts.

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