It's a very mild abrasive and won't harm the bore. Just make 10 - 15 passes through a well-oiled bore, toss the patches, and oil the bore up again. The Kroil (penetrating oil) will soak into/through the crud, and the J-B paste will clean it out. When the patches quit coming out black you're done (could take a very long time depending on how well the bore was cared for). Neither of these products has ammonia. During this process I usually let a heavy application of Kroil sit overnight, clean with J-B for as long as I time allows, then put another heavy overnight coat of Kroil on. No harm to the rifle.