I think that the grease in the bbl and a good rod and smack it should do the trick.
I have not had to do this very much, but a few times. Works good, FM
I would remove the barrel from the upper receiver, chuck the barrel on a lathe and using a short spade drill (minimum flexure)peck at the center of the obstruction, once the material is removed it should collapse somewhat.
If you have no access to a lathe I would use a soldering iron and burn a hole through it. It will smoke!