I use white board chalk sticks in combination with any oil to remove light rust film from damascus or steel barrels. First coat the barrels with a light film of oil. Next rub the exterior of the barrels,focusing on the rusted areas,but for preference the entire surface, with the chalk stick. You will soon see that the rust is lifted by the chalk sticks without damage to the barrel pattern/finish. Wipe clean with a soft rag and repeat as required. If the problem is pronounced you may have to repeat for several days until all of the rust has been removed. This is a very old trade process used to polish metal.In my experience the results can be surprisingly good.Please note this method will not remove sub-surface pits.
