It is what I use for general bore cleaning. It may take more patches, but another product that will remove the copper and which will give a strong blue color change is Boretech Eliminator.
Spanish mauser barrel Patch#
If you are unsure of your results, you can patch out the KG-12 and apply a cleaner that changes color in the presence of copper just to see if you are done yet. It doesn't turn blue or green-just gets darker orange brown-as it picks up copper, but its fast and its capacity for copper is enormous. I put a sloppy wet patch through and let it sit 15 minutes and repeat once. Once the carbon is gone, you'll want to flush the bore with boiling water to remove the Carbon Killer or with a solvent like denatured alcohol or Gun Scrubber to remove the Gunzilla. Repeat until you stop getting carbon coming out. If you are less patient and don't mind using a product that can hurt finishes, then get some Slip 2000 Carbon Killer, plug the bore, fill it with the stuff and let it sit 15 minutes, drain the stuff back into its container (it's still good) and patch and brush it out. It can take several weeks for the carbon to stop coming out. If so, I repeat and keep repeating until it stops coming out. If I have a heavy build up like yours, I'll let the bore stay wet with Gunzilla for a week between patching and bronze brushing to see if carbon or rust comes out. Something that I find loosens carbon and rust well is Gunzilla. Especially if they were fired with corrosively primed ammunition and not properly cleaned afterward. Guns that have not been properly maintained can develop enough carbon and crud build-up to fill the grooves. If the rifling seems to be gone all the way down the bore, then you'll likely find it all magically reappears when the bore is subjected to a proper cleaning. If the rifling is gone only at the muzzle, then the counterboring suggestion applies.