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.