That sounds like one of the older breech plugs because you can change from a #11 or musket cap or even a 209 primer with the right plug. I just purchased a breech plug for my staghorn. Not that I needed one, but the other one has had hundreds maybe even a thousand shots through it, and still it shows no wear. That to me is not normal. So since I had to purchase my one dollar screw, I ordered a breech plug from them at the same time.

If it is the breech plug I am thinking of..



the one end removes the nipple and the other end remove the breech plug. It comes with a small breaking bar and an allen wrench to remove the necessary bolts.. is this theone you need? Those are the CVA parts numbers. You could make one from some round stock if you are handy...