I use the cold blue called OxphoBlue from Brownells. Use the directions supplied. I prefer the liquid to the paste. The material is applied and then rubbed off. Before reapplying the area is buffed with steel wool to burnish the metal. If metal was actually moved on your rifle this won't help, but if it's just a minor scratch in the bluing it will camoflage it to some extent... A lot depends on the depth of the scratch, but it should help some..