You do not plug the barrel, just squirt it in untill the foam comes out the muzzle. Let sit for 20-30 minutes and run patch thru. Then light brushing and repeat. Run 3 or 4 more patches thru and it comes out clean. Dry and oil. Stand upside down and let excess oil run out the muzzle and you are done. Works great. Have found it at local Fleet Farm and also Gander Mountain carries it in my area.