Shotgun barrels are smooth. Rifle barrels have lands.
I have seen for myself a Colt M16A2 barrel that was eroded so bad from a well meaning Marine using the same method that he had to pay for the unauthorized damage done. He had it clean alright, right past the chrome and into the barrel steel.
Incident happened in Lima Co, 6th Marines, 2nd MARDIV. Rifle was elevated to 2ndFSSG for rebarrel after being coded out and the Marine recieved a statement of charges for the cost of the new barrel as well as a Art 15.
Yea, just keep right on grinding your bore with that drill