yes it has a hex head on the breach cap
Breech cap? End cap? Not sure which one your referring to.
I don't have a CVA Staghorn, I do have a Traditions Timber Ridge in line, which is similar to yours. Clean barrel using whatever bore cleaner you normally use to remove excess fouling.
A stuck breech plug can usually be removed by using one of the following cleaners; Ballistol (buy in any gun shop), Kroil, PB Blaster (in automotive stores) or Liquid Wrench (plumbing supply stores). The first thing you do is, plug the breech end primer hole with a piece of modeling clay, and spray or pour one of the above cleaners into the barrel, tap the breech plug a few times to set up vibrations, let soak for a day (tap breech plug whenever you get a chance). The next day try to remove the breech plug. I know you know this but, remember turn to the left to loosen. If this doesn't work, repeat procedure, it will eventually come loose. Have patience. If it comes out, remember to clean the modeling clay out of the primer hole, then complete cleaning of the gun.
If you meant the cap covering the end of the receiver, use the same cleaners, spray the heck out of the end at the gap where the parts mate. Repeat the tapping and trying to loosen procedure, remember, it will come off eventually.
If it was the breech plug, I recommend that in the future you use a better anti-seizing paste. I use automotive anti-seize paste, the same stuff that is used for spark plugs. Just don't us too much, otherwise, you might block the flash hole, and then your gun won't fire. A word of caution, Both Ballistol and PB Blaster give off a "smell", the wife won't like it.
Let us know how you make out.
