I don't like to see folks usin' alcohol in their barrels without tellin' 'em they oughta put some kind of non petroleum based oil in the barrel immediately afterwards. Any vegetable based paste lube will protect the steel from rust, and won't degrade your powder. TC's Bore Butter, bear grease or even plain old Crisco will work. Petroleum oils combine with black powder residues to make a really hard to clean fouling.