I would try the PB Rust Blaster too. That is pretty amazing stuff. Just give it time to do its work. One it works for a day or two, when you put your removal tool (screwdriver or whatever) on the breech, give it a couple smart whacks with a mallet. That might be enough to vibrate the rust loose in the threads. And, another tip, once you get it started, continue to spray it with the PB and work it a little at a time, back and forth (or in and out) whatever you prefer.

Stuck breech plug
 

Well I got mine unstuck... I soaked it with wd40 over night and nothing... so I heated it up with my propane torch and then sacrificed a 9/16 spade bit by grinding off the tip so it was like a big screw driver, then put it in my impact drill and got it out. The impact drill didn't work until I heated up the breech plug. Thanks for all the help guys.

The easiest way I have found.... you do not mention what kind of rifle it might be, but for me I strip the barred action down- remove the hammer and trigger if possible. If is scoped remove the scope.


Then immerse the barreled action in boiling water. Make sure the there is enough depth of water to reach above the breech plug a few inches. Let action sit in the boiling/boiled water for several minutes. Expansion of the barrel will allow water to work on the fouling residue in the threads.


While still really hot remove the barreled action and place the recoil lug in a vice - pad the lug with a heavy piece of leather or a couple thin strips of wood, tighten the vice and then with the proper tool try removing the BP.


It might take a couple of attempts but it will come..