These can be stubborn to remove. Take the above mentioned advice. Sometimes soaking the joint with a thin lube helps. Another method is to get a can of Dust-Off spray, invert it, and spray the barrel just in front of the receiver with it. Also give a spritz up the back of the breach into the bore. The extremely cold liquid will allow the barrel and its tenon to shrink a bit before the receiver does. You need to work fast before the two metals transfer the cold between them. If you heat up the receiver joint with a hot air gun a bit before you do this, it also helps. Make sure to wipe off th barrel afterwards inside and out because that cold will allow moisture to condense on the metal afterwards.
