My experience with BP barrels is that if the last 4" or so is good then it will shoot ok. From there you are able to tweak. I had a Swedish 12.7x44R that looked like a sewerpipe due to corrosive primers, BP and lack of cleaning, but it would shoot to les than 2" at 60yds all day long.
Take a feel along the barrel at the 7" mark, if you can feel a slight lump then a stuck boolit was shot out at some time. With wads and a grease cookie you can make it shoot "just" as good as new.
Dont dispare friend, youre not alone!