Counter boring is extremely common in surplus military firearms where the rifling at the muzzle is drilled out allowing a “clean” muzzle most commonly seen in mosins can look up pics , but OP you’re definitely gonna spend way more money than what a barrel is even worth just to do thisSo, if that rifle barrel's bore is worn and its rifling eaten-away with corrosion or worn thin from use or improper cleaning.... you think a gunsmith can grind down the bore and get more good rifling from somewhere, hidden in the steel?
Sounds like what that rifle needs is a new barrel.
Or, if you have a gazillion dollars to spend, the old barrel could be sent to a custom barrel making factory to be drilled out and rechambered and re-rifled to a LARGER caliber, so you'll have to buy or start reloading some different ammo.