Yes, what JimboH stated about trying to get it out while the barrel is warm is great advice. Heat makes metal expand, the heat transfers to the greatest mass. The barrel with retain the heat longer than the breech plug. Thus the threads in the barrel will be expanded a bit longer than the breech plug. This expansion is ever so slight, but its probably just enough to make the task easier. On removing bigger objects, often a torch is used to heat the surrounding area and then ice is applied to the object to be removed. Heat expands the outer area and the ice contracts in object to be removed.
Dan