Friends:
Actually, if we tear the head off the case, then the primer and powder are gone and the problem is MOSTLY solved. Then we use a stuck case remover ( also called a broken shell extractor) to remove the headless case.
At least I hope so.
GKT
This was my own thought process when removing the stuck 243 cartridge from the old M70 barrel. I would simply cut away enough case-head metal to allow me to either grasp the remaining case head firmly or else to remove the case head entirely to allow the powder to drop out.
Good thought, but I failed to realize that using a hand grinder to remove the case head metal would generate heat. Fortunately when the primer fired, it blew straight out of the primer pocket and didn't set off the main powder charge. Also fortunately, I had the sense to keep everything valuable out of the way of the bore line and so the primer didn't hit me in the eye.
That happened 40 years ago and I was extremely lucky. YOU need to be extremely careful!
Regards, Joe