There are gages out there that have interchangeable tips, like Starrett. You just have to make sure your needle size threads match the ones you choose. The disadvantage of trying to measure a pit/s is that the needle will get into the pit and if you are rotating the barrel watching the needle, it will move the zero point.
Take a bright flashlight and look down the barrel if the pit/s look dark they might be deep, if a greyish cast, I wouldn't worry about them.
If it still bothers you go to a field that has very low grass, fire a shell and watch for the wad, if the was is not all chewed up from catching on deep pits, again don't worry about it. AND don't hone anything, more barrels have been ruined by honing.
