I bought a used rifled barrel for my shotgun. It's nice but has what I THINK is plastic residue "stuck" to the inside of the barrel. It's not a war stopper, but I'd like to remove it just so it doesn't build up even more thru use. I've tried everything in my cleaning cabinet, including Lacquer Thinner, ammonia, Shooters Choice, Hoppes #9, yadda yadda. Wire brushes on a drill motor won't take it out. Anyone have any ideas? I sure would appreciate any advice.