I doubt that any commercial producer has ever done as much research and development work on firearms cleaning products than the US military. If you want really good stuff at very reasonable prices watch on-line sources and gun shows for GI surplus "Rifle Bore Cleaner MIL-C-372B & AM 2 6850-00-224-6657", manufactured for Uncle Sam by Phipps Product Corporation, circa 1960's to 1970's. Usually seen in 1/2 pint or 1 pint OD green metal cans. Typically a buck or two per can.

Nothing better for heavy fouling and removing copper residue in the bore, bolt, gas cylinders & pistons, whatever. This is what we used in the Army for pistols, rifles, machineguns, all of the small arms.