Carbon build up??

[Patrick Chadwick]

Unfortunately - yes - that's corrosion and pitting. Using a borescope will only discourage you further.**
And leaving the bore to soak in aggresive chemicals can cause further pitting underneath the hard deposits!

About all you can do is to smooth it out. May I suggest that you take a look at this contribution?

https://www.milsurps.com/showthread....ight=challenge

Otherwise, I can only suggest bore-lapping.

Give the above-mentioned methods a try.

Good luck!
Patrick

** I have an original Winchester 94 in 32-40. An expert with a borescope told me it was scrap and I should pass it on to a collector. I ignored his advice and continued with my methods (see above). It now shoots better than most modern replicas, regardless of how it looks.