Anyone know what range I can expect out of the Swivel? The Nevada Desert is my backdrop , but Im very curious.
Your mounts are really nifty. I like 'em. However, to be honest, I think they may be a little lightly constructed for use with your barrel and a lead ball. I'd be a little more concerned about recoil than range at this point.
I see you have a lanyard lock on your bbl. If you're gonna be yanking that while holding onto the tiller with the other hand with a lead ball loaded, you're a braver man than I. You might look into adding a more substantial grip.
I'd start with a golf ball and ~100 grains of FG, then heavier charges until you get a feel for what it does before trying a heavier ball. Another member here has found a source for steel balls to fit a golf ball bore. I'd try those before lead (Personally, I would never even try lead on either of your mounts unless I fixed the bbl so it couldn't swivel, and fired them with a fuse or long lanyard).
I'd add some kind of a vent sheild if I were holding the tiller when it goes off. Have a look at a few pictures of what comes out of the vent on a cannon that large.
The above is JMHO. I'm not one to poop on anyone's party, but I want
all of us to stay safe.