Tad Houston, I had one of these back in the early 70s. I was hoping someone who was using one now would respond, so we wouldn't have to rely on my 20 minute memory, but it looks like that is all we have.
I never tried a minnie ball in mine, because they weigh about an ounce and a half, and I found the round ball at just over an ounce supplied enough recoil with any meaningful powder charge.
While I don't recall the measurement, I used a round ball cast in a 69 caliber Ohaus mold. It did fit a little loose in a clean barrel, but not loose enough to allow a patch. To keep it in place, I forced a 12 gauge card wad over the ball. I found that ramming subsequent balls was quite difficult, unless I put a dab of Crisco on the down side of the ball, to keep fouling soft.
After the first shot, the ball fit better in the bore, and I would omit the over ball wad, unless it was going to be carried a while before shooting again. I'm sure you know how important it is to keep that ball against to powder, to keep it from acting like a bore obstruction !!!!
I don't remember the charge I settled on, but I do remember starting at 20 grains of FFG, and working up until I was getting enough apparent power and recoil.
What I mainly loaded mine with was 3/4 once shot loads. I used 12 guage cards (tough fit at .730) over the powder, 16 guage (.670) fiberfelt cushsion wads, 3/4 ounce of 8 shot, with two 12 guage cards over the shot. If memory serves (it don't always), 40 grains of FFG took teal over decoys, at about 25 yards, when I did my part correctly. Once again, for ease of ramming, I used Crisco on the bottom of the over powder card.
