Do not try to unscrew the breech in a CVA or Traditions gun. The breech plug is cross threaded with the touch hole housing or percussion drum, and then drilled open from the muzzle with a deep hole drill. You are more likely to break off the button/hook/tang than to unscrew it. Even if you could, because of the cross threading, you won't get it to go back together properly. It is a particular breech system used by their manufacturer, Ardessa in Spain. It makes a very strong breech, but has draw backs.
A TC can be unscrewed, with a great deal of fuss and then replaced. A CVA/traditions is a whole nuther beast.