Picked up an XP 100 at a gun show. Just happened to have a new box of ammo with me. When I inspected it (just a quick look) I noticed rust in the barrel in a few spots. Stopped on the trip home and fired a "few rounds". No more rust.
Yep! that Iron Oxide riding down the barrel imbedded in a piece of copper and lead at 2500 FPS will clean that rascal out