I recently bought one of the FN 20" NOS uppers and while running some patches through the barrel, they continually come out green. Typically, I would associate this with copper fouling, but these are supposed to only be test fired and the barrel rifling supports that. The barrel was pretty dirty, but a couple patches and the rifling looks perfect, strong and shiny just like my other brand new uppers.

I ran some slip 2000 solvent patches through it and then some slip 2000 oil, but they still came out green. I did not run any copper solvent through it.

Any ideas?

Thanks!

Plastic or brass jag?

Plastic. I made sure of that when they kept coming out green.

Who knows how long it had been sitting in there, and with it being a new barrel it was/is probably rough.

Plus I bet if you have used something designed to remove copper it would have cleaned up faster.

CU+2 is the best I've found, then probably Butches.