I recently got a Mexican Mauser rifle dated 1937. I noticed that when cleaning with a brush or a patch, the drag along the length of the barrel is not constant. About 4 inches back from the muzzle, the drag on the brush goes way down. Ahead of that point or behind it the drag feels normal. So I put the calipers on the barrel. The suspected bulge measures .695 inch diameter and the places in front or behind measure .687 inch diameter. Is there a way to correct this or just let it go. I cannot imagine that it is an improvement to the gun.