Black powder shotgun barrel pitting ?

[Old smoking pole45-70]

I was given a CVA black powder shotgun and the barrel is badly pitted, I used emery cloth medium cut with oil to clean it up twice to see how bad it is, it shows bad pitting half was down the barrel as far as I could see. I have miced the barrel from choke down the length of the bore mic length and it's .720 the barrel seems heavy and thick walled. How much is to much to cut out to be safe to shoot.

 

[bang]

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