I recently aquired an old Enfield M1917 and on first glace it looked like a used but solid rifle, but after a closer look and with a brighter light I noticed that there was a massive amount of build up in the bore. I use Boretec: Eliminator solvent and after several passes with that on a swob and a brass brush and a foaming bore cleaner (that I barrowed from a friend) there is still more in the bore. I am sure that it is buildup and not pitting. Guess I was looking for some ideas from some of the more experienced on here.
Try plugging the barrel at the muzzle, stand the rifle on its muzzle, and fill the barrel with Kroil. Let it sit for a while, and clean it with a bronze brush. If necessary, repeat, letting it sit for a longer period depending on the amount removed the first time.
When clean, lightly oil and should be OK from there.