Thanks Ack, I JB'd the barrel Friday, cleaned up nice, I have tooling marks running lengthways like the rate of feed was increased as it was cut, or dull. With a borescope, you can visualize it is an attractant, I'd complain if it did not shoot, but it does. I can clean the barrel, it is a gun I built for my Godson, not a heavy use rifle, we sneak out when we can, between his activities.it is a thing, Milo. Also, I do not go the long shooting strings that you do. I found varget to have a pretty good carbon ring.
You may try the user friendly Montana Extreme Copper cream that is very easy to use compared to JB, and more agressive Iosso and flitz.
I use the Copper cream on patches or on a really foulded up barrel with a bronze bristle brush...you will love how easy this product is to use. Short stroke on 3 patches will usually clean out the copper and carbon if the regular brush has not cleaned as NICE as you would like to.