.... Anyone know how to remove the plug from one of Hugh’s barrels? Thanks.
Hugh does!
Otherwise, a tight breech plug requires the barrel be clamped in a good strong vise mounted to a heavy fixed workbench.
As Bob suggests, it's fairly common practice make a breech plug wrench to fit the bolster or to grind the jaws of an old wrench you might have laying around so that they are the same angle as the bolster's sides. You may even need a "cheater" in the form of a pipe or something to add length to the wrench to deliver more force.
If your worried about marring the bolster a little marring can be filed out or you could bend some sheet brass around it....and, by all means, avoid the having the wrench reach so far up on to the bolster to where its jaws straddle the tang, elsewise you will mar the tang sides.
Haven't had a breech plug that didn't come out yet....even a couple that the threads were pretty galled up on.
Enjoy, J.D.