with my new rifles i always use a barrel break-in proceedure that includes two sessions with jb paste. this product will lap a clean bore and is a great help on stubborn fouling with used guns.
for my bolt and leverguns i work the bolt and lugs with jb and cycle the action for a time. this results in a better mating of the parts ( as evidenced by smooth shine ) and a slick action.
clean up is easy with any solvent.
i learned this proceedure from boots obermeyer while in sniper school, and it has been a help with new AND used rifles.