PBblaster is a deeppenetrating oil like the other guys said. I took the barrel off and and soakedthe choke endin aboutfive inches of PB blasterin a cup overnight. I think a big thing that helped free it was hitting/tapping my wrench with a hammer while trying first to tighten and then while unscrewing. I think this would be alot easier with two people if you can get help. good luck.

Chris