this is just an educated guess, but that crappy ammo was probably way undersized and/or way too soft an alloy and just smeared all the way down the barrel. id get some cheap metal cleaning picks from harbor freight, a good desk lamp, and start scraping. When you get a good amt of it out, switch to chunks of chore boy copper scrubbing pads , wrapped around an old bore brush and clean it like nuts I cant imagine how bad the leads of the rifling and chamber are