If you are looking to buy a C&R gun, you will probably run into the 'dark bore' description. These guns can have a lot of dirt built up in the barrel. When you get it, you 'clean' the barrel before shooting.
You will see a lot of dirt come out and eventually, you will get patches that look clean.
Then you shoot a bit and as you clean, you wonder where the black came from on the patches as you did not shoot a ton of bullets in there.
Old miltary guns, with that build-up, will still have built-up crud under what you took off. Firing the gun will heat the barrel and loosen some more of the crud.
One of the things that you can do to help the process is to get one of those foaming cleaners and foaming copper removers and use that. Then, after you take that out, run a solvent soaked patch through the barrel and let it sit for a while, then attack it with brush and patches, and do it over again. Eventually, you will get the gun to the point where it is almost clean as new, and then, you can see what kind of pitting you have, or not. Just depends on the luck of the draw.
The Doc is out now.