I used acetone, based on what U Pol recommends, but I cleaned the gun immediately after each use, running acetone through the pick up tube and through the gun. I then wiped down the gun with an acetone soaked rag to clean up any remaining bedliner.
If you let it dry in the gun, I think you'll be buying a new gun.
SMB-less as of 02/04/2012. Our savings account is richer, but our adventures are poorer.