Got the cases made for this gun.

Ended up looking most like the 33mm case size, the brass measures that many millimeters from the breechface end to the case mouth.
I'm running percussion caps, two and three quarter drams of GoexFF, milk carton 'cup wads' made in my lathe by pushing 10ga punch size card wads through a special die with a special punch to form little gas seal cups, and saddle felt doughnut shaped wads soaked with bore butter. That all's topped with the 411 grain roundball made from pure lead and cast in the little pincher mould from my cased Mahillon set. It ends up being a slightly compressed load and feels right as it comes together.
I'll be shooting it tomorrow morning at dawn out at the ranch.
Wish me luck.

--Tinker