So, this isn't aftermarket, it's a factory 223 barrel that I bought used, but I didn't want to post in 110 tech for fear of missing out on advice from non-110 users...

I bough a used 223 barrel here and it's one of the dirtiest I have ever seen. I am not getting any copper out of it, but it will NEVER come clean from the black, and I see what almost looks like rust bumps inside the barrel. Those appear to be coming out some as I scrub. I think I have already gone through over 100 patches over the course of 2 weeks. I have been soaking overnight with Shooters Choice until I ran out, now I'm soaking nightly with Hoppes #9. Almost daily I scrub with a nylon brush and a few passes with a tight bronze brush. This releases a ton of black. I put a few more wet patches through and then let it sit over night. I have done this for many many days now, and I do think it's getting somewhat better... mostly towards the chamber end.

I have also tried something a bit different here (since I don't have high hopes for this barrel), I have run a few patches of Flitz metal polish through the barrel. Those come out black as night and smelling of freshly burnt powder. After that, it appears to let loose more black... so I scrub and scrub.

What else can I do? I'm thinking about getting a stainless brush to see if that helps. Is there any chemical that I should try? Any mechanical gadgets or processes? If the answer is to scrub more, then I'll keep at it and maybe put this on an action once it's clean, 6 months from now! I know it will never shoot like a dream, but I just want it as good as I can get it before I mount it to an action.

Thanks for any suggestions!