had this problem this fall, go to a gun shop and git a can of Break Free. Break Free is what the US military uses on their guns and you can git virtually anywhere, i found it at walmart. anyways empty it into a glass or cup and set the barrel in the cup upside and make sure the choke is submerged. let it soak for a couple and take it and lightly tap the barrel to knock the crap loose and keep it soakin. after a week or so it should come loose.