Hydraulics is your friend.
Jag on rod, into the muzzle, lower until it touches, mark your rod. Fill the bore partially w/Kroil. Now, get a very tight patch onto the jag and work the patch/jag down to create hydraulic pressure. If you're getting too close to the mark and you haven't popped the case out yet, remove the whole works, tighter patch, more Kroil, rinse-repeat.
