[gundisalvus]

Hello. I am new to FN and recently purchased an FN 509 midsize tactical. It is my first pistol with a threaded barrel.

I put 300 rounds of Remington target practice ammo through it today for the first time. I noticed afterward that the cap on the barrel came loose and that the threads and crown were light gray and brown, as if they had rusted--which I can't believe. But I tried CLP and it is still there.

I have never seen this before on a gun. Is this normal for threaded barrels? How do you fix it? The pictures don't do justice to how light the barrel looks now, even after hard scrubbing with CLP.

 

[street doctor]

its gun shot residue from shooting. most people take the thread protector off when shooting. it won't cause any issues at all. it just takes some scrubbing to get off if it bothers you. most people just leave it alone.

 

[gundisalvus]

its gun shot residue from shooting. most people take the thread protector off when shooting. it won't cause any issues at all. it just takes some scrubbing to get off if it bothers you. most people just leave it alone.

What do you recommend I use to scrub it clean? Like I said, I have never encountered this before on my other guns!

 

[Maynard]

What do you recommend I use to scrub it clean? Like I said, I have never encountered this before on my other guns!

Carbon remover

You can also use a die to keep the threads looking new. Word of caution here, try to get most of the carbon buildup off before using the die and be sure to use oil/cutting fluid if you are cleaning the thread up with a die.

1/2x28 Die

 

[gundisalvus]

Carbon remover

You can also use a die to keep the threads looking new. Word of caution here, try to get most of the carbon buildup off before using the die and be sure to use oil/cutting fluid if you are cleaning the thread up with a die.

1/2x28 Die

Thank you!

 

[Gary1952]

When I go to the range,I just take the thread nut off on my FNX45T

 

[GarrettJ]

You can also use a die to keep the threads looking new. Word of caution here, try to get most of the carbon buildup off before using the die and be sure to use oil/cutting fluid if you are cleaning the thread up with a die.

Threading dies are made to do just that - to cut threads. If not careful, you can start removing steel from your threads with them, giving you loose, sloppy threads. Not a big deal if you never use them, but can cause issues if you want to use a silencer on your barrel.

I leave the thread protector on so it can... protect the threads. To keep it from backing off you can either use an appropriately sized rubber O-ring, or wrap the threads a couple times with Teflon plumbers tape.

I’ve been using the plumbers tape trick for a couple decades to keep silencers and thread protectors in place.