I to have in the past had this problem. I have also corrected it for many shooters.
First start with a clean barrel, specifically the theads and the breech plug itself. I mean spotlessly clean, this is a ground zero starting point. I have used many different greases, tapes and even crisco to try to stop the breech plug from welding itself into the barrel. I like gorilla Grease form T/C, but any good grease preferably a high temp grease as TOGO suggested.
Now, there is no reason to put the breech plug in with a 6ft extension at the end of your biggest breakerbar. Doing so is only looking for trouble. Snug is good.
I personally clean my barrel, at the range, after every three shots and remove the breech plug and clean after every 20 shots. I have yet to have a problem with removing the breech plug from any of my black powder guns regardless of the propellant used.
For me a black powder rifle is a tool to allow me to hunt more/longer. I do not shoot it for recreation. I will take it out every year and shoot 10-20 rounds to be sure its still zeroed from last season, but thats about it.
try it, I'll bet it will solve your breech plug woes!!
Good luck,
CW