I’d run some JB bore paste on a tight fitting patch soaked with some kroil over and see what happens. I use a brass/bronze brush 1 caliber smaller than the bore to hold the soaked patch.
Just curious what kind of rifle is this and how many rounds fired?
The rifle was my grandfathers. It was customized or transformed .30-06 M1903 Springfield from WW1 or WWII by a gun smith named Vickory (Boise Idaho). Purchased around 1950 and probably has at least 1000 rounds, I shot my first muley in 1983 with it.