Brand new shilen barrel on a custom build. Barrel had never been fired. I shot 20 rounds through it and noticed a tight spot about mid way through the barrel, between 10-11 inches from the breech.
I use my lyman bore cam to see what is going on and I find this:













This area is only about 1-2 inches long. The rest of the bore looks fine/has no copper. I have been using foaming bore cleaner, sweets 762, and some VFG pellets with JB bore paste on them. Nothing seems to be doing anything to this thick galling. I have never had a bore with copper in it as thick as this, especially after only 20 rounds! Any time I have had copper in a bore, a quick treatment with JB bore paste cleaned it right out in no time. This stuff is on there so thick, I am at a loss of what to do with it. You can feel this spot when pushing a patch down the bore with a cleaning rod. It feels like "rough" or "slightly tight" spot in the bore because the buildup is so thick.
Was shooting factory ammo (S&B), so it was not a super hot handload or anything.
I am at a loss for why this happened after 20 rounds, and how to clean it out.
Any suggestions?

Barnes CR-10 will definitely remove the copper, unsure if safe for SS.
Brownells J-B bore cleaning compound is safe and very effective
Brownells J-B bore bright

Plug chamber with rubber plug,,, go to grocery store,, in the laundry aisle, and grab bottle of ammonia..

Fill bore of barrel and leave sit couple days,, rinse and repeat.. see if that helps

Only other option be to use RCBS ?? devise that essential use electolosis to remove copper from bore to and electrode (simiiar to electro plating_

I wouldn’t worry about the copper so much as the rough rifling.

I would lap that barrel to smooth out some chatter marks.

Send pics to Shilen and ask their advice.