I don't even play a gunsmith on tv, but it occurs to me that if the bulled could be drilled through from the bore, in a careful manner that protected the barrel, then penetrating oil could neutralize the power and make things much safer to work on. I would let it soak in kroil or the like for a long time before trying anything.
Another reminder the top end can fire by itself. Don't give up, take your time, and be careful. Good luck.
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