Take a piece of brass rod about 1/4" diameter and long enough to reach from the throat of the chamber to the rear of the stripped action. File a long angle on one end of the rod to come to a sharp point at the "muzzle" end of the rod. With the action held in a padded bench vise, use a light hammer to tap the sharp end of the rod between the case and the chamber, just as though you were using a chisel on a piece of wood. Since the rod is brass, it won't hurt the chamber. The case will fold into the interior of the chamber, and you should be able to get it out with a cleaning rod and bronze brush. It may even come out when you remove the brass rod.