Thanks for posting!
Do you have information as to how the gun remaining in such amazing condition for 150 yrs.?
Was it Nitro Proved at some point?

BTW: the barrels are English 2 Stripe
'Zipper' weld between straight ribband end welds

[Linked Image from photos.smugmug.com]

According to Bro. Helsley, the barrels on Best grade were labeled in the Powell ledgers as "Best", and were usually 3 Iron. Other grades were simply "Damascus" (usually 2 Iron) or "Stub Damascus" (usually Laminated Steel).

Tiny superficial pits are not uncommon and were usually from surface inclusions lost during the finishing process. I tried to enhance your image and there are a few more nearby. I can't explain the loss of contrast in that area, other than possibly from light rusting that was successfully scrubbed away. Do you know if the barrels were ever rebrowned?

[Linked Image from photos.smugmug.com]

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