Daryl-

That thing's a beauty.
I love my sixteen bore double rifles. I'm running .666 balls in one of them, and just got a mould marked to throw .678 balls, I suspect that with pure lead things are gonna be a bit smaller though, and I hope that's the case. I'll be pouring lead in a little while today and will know for sure.

Six drams is a lot of powder!
I'm running in the nieghborhood of 2-3/4 to 3-1/2 drams, one rifle takes more than the other does.
I wonder what your muzzle velocities are with that much FFg...
What kind of MV are you getting outta that thing?
What accuracy are you getting with it?
What is the rate of twist?
What are the bore/groove dims on that barrel?

When you tire of that heavy old iron, you're welcome to drop me a line and arrange for shipping it to me too...

--Tinker