M*CARBO Brotherhood

The 509 Spring Kit is a ray of light for the FNS owners


I do not have an FN 509, but I have an FN FNS.
While it has a lot of positive aspects, IMO, it was a few negatives. The worst one is the obnoxious > 7 lbs trigger pull. I guess the lawyers in Belgium have even more power than in Austria. :slight_smile:

I could shoot the gun, but it is painfully annoying to wrestle that trigger. I was on the brink to go and trade it in an LGS.

After watching several videos on how to disassemble the FNS and the 509, I concluded the relevant for this thread internals are the same or similar. So I decided to risk it and get the M*CARBO 509 kit for my FNS.

The installation was effortless following the videos. Everything fits perfectly. The original sear spring was with an older design - it hooks in a small hole in the sear. However, the new one works just fine. It uses the other side for support.
The results are fantastic; the trigger pull weight dropped by 2.5 lbs.

I believe it can drop even more (say 1/2 lbs) if I polish the internals properly.
When I disassembled the gun, I was amazed by how roughly machined are some of the parts. The striker has a hard time coming out of the channel, and the sear leg was scratching on the sear cage(or whatever its name was). I took out some of the roughness, but I did not spend much time on it, as I was very eager to finish the spring installation.

To be honest, I have not had the chance yet to fire the gun at the range. In the worst possible case, if I am getting light primer strikes, all I need to do is put back the lawyer friendly original striker spring. If that brings the trigger pull weight by a pound, it is still a pound and a half reduction.

The bottom line, this kit is a must for the FNS owners. Probably the same is true for the 509 owners, but I have no first-hand experience of how far the lawyers were able to influence the trigger pull.

To preempt the FN fanboy comments - it takes zero effort to ignore the thread and continue using the stock springs.


@MasterJP Welcome to the Brotherhood. Feel free to post here and introduce yourself to the rest of the crew.

While I understand where you’re coming from, you won’t find any bad behavior on these boards. You’ll find this place is a bit different and we don’t take kindly to that type of thing here. We like to keep things civil and helpful, though everyone is entitled to their opinions and free to voice them in the proper way.



That is great to hear.
I see no value of people always replying that the stock trigger is perfect, and nothing beats FN (or Glock) quality.
MCARBO (or any other company making aftermarket performance parts) is not forcing anyone to buy anything. However, they will not be in business for very long, even less introducing new products if nobody is buying from them. Simple proof there are a lot of people like me finding great value in these improvements.
Now, does that make me a M
CARBO fanboy? That is a fair question. Guilty as charged, I confess your honor. :grinning:


I doubt Chris and the other folks at MCARBO will be upset about that. Gotta vote with your dollars, if you like what they make and the way they do business, then that’s where you spend it.


im upset about 1 thing. and i gotta put it out there.
they dont do a kit for the FNH Five seveN yet.
I will be waitin patiently over there in the corner, for 5/7 and PS90 parts to make things more better… :crazy_face: :+1: :+1: :+1: :+1: :+1: :+1:


If we are going to have a wish list, I have three things to add:

  1. FNX-45
  2. FNX-45
  3. FNX-45
    The trigger return spring (the one you can see in the trigger when you look from the top of the frame with the slide off) is 2-3x heavier than what is necessary. One can see how much it adds alone when the safety is engaged.
    I would guess the story is the same with FNX-9 and FNX-40, but I have never tried them.

M*CARBO, please do something about that.


@MasterJP welcome to the forum ivan and merrychristmas and a happy new year



Thank you for the kind words, and all the best to you too.
I have been a member of the forum for about two years (IIRC) now. Until yesterday, I did not have something as exciting as this cross model application. I was lurking in the shadows. :smiley:


@MasterJP Welcome to the Brotherhood


@MasterJP Welcome aboard