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Threaded barrel maintenance

790 Views 7 Replies 5 Participants Last post by  Gary1952
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.

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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.
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