Well, after the Zimmer thread, I couldn't stand it any more. So, I worked a few days figuring out my own version.
It's all shown in the picture.
1. 8.15x46R case.
I bored it out for shot gun primers. I didn't use standard primers because I didn't want to use re/de cap tools. The other reason is so I can just push the shot gun primer out with a pencil and recap. The primer is drilled and reamed #C (.242). A few thousands of the primer is out side the case to capture it and seal it against the case with the breech block. The case is chamfered at standard 82 deg.
2. The ball.
I have a coffee can full of buck shot (.330 dia). My groove is .316. So, I thought it would be a good diameter and would fit the throat well. It pushes into the case and will stay there while I put it into the lube (Darr) much like you lube the Zimmer balls.
3. The load.
I was hoping to just have to use the primer but, the ball wouldn't exit the barrel. So, I have some old bulk smokeless and tried .3cc (Lee dipper) of that, it was very dirty and to fast

Next, I took a dip of B'eye (2.5 gr) Burnt clean but way to fast

I drilled out the dipper and threaded it 1/4x28, screwed in a 1/4" long set screw, even with the bottom. It gave 1.7 gr B'eye, still a loud crack

Threaded it deeper and adjusted it to dip 1.0 gr B'eye (as pictured), went out and tried it, no crack and fairly clean

I can hit my little swinging targets at about 40 ft.
I'd be happy to answer any questions.
Frank