Don't know details, rifle was bought with two barrels, and I put new one on with this unexpected finding. Not much cleaning on the new barrel since it has only couple of hundred rounds on it. But when I clean, I use Hopes 9. In my experience, it works better then the Fancytech cleaners.Looks like corrosion to me. I did metallurgical failure analysis for 45 years. I wonder what the alloy is. You have no choice keep shooting it. What do you clean the bore with?












