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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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When I go to the range,I just take the thread nut off on my FNX45T
When I go to the range I remove the thread protector. Also installed a DPM recoil spring and it does what they claim.
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