Tom - you might find the smaller, lighter 11 bore ball hits closer, ie: regulates more easily, just as I found that in my 12 bore that liked the 14 bore balls - centrally supported by the gas-check 'cups'. I must note the early success in my loads, which stopped further testing by me. That testing could have helped others today. Now, much of that is speculation of things that might help - things we might have tried but need to be attempted now.

Kiwi bloke brought up a good point about using smaller diameter wads inside normal shotcups to give height to the balls. The guys did this in their 12 bore ML shotguns, using .58 cal balls inside the plastic cups. I wanted more ball weight so I only tested these more than once, about 35 years ago.

If a ball inside a shotcup gives good centreing (a tight fit) in the bore, then that is another variable you can test.

I have read that a shot cup actually rotates in the bore in the direction of the reamer, which would be right handed if reamed from the breech, left if from the muzzle. This came from an article on trap shooting, where they were attempting to get the very best patterns and that the minor rotation actually screwed up that was capable with slight longitudinal grooving. I cannot remember where I read that, now - dammit.

The actual direction of reaming is not important, but that ANY rotation should aid in accuracy. The longer the wad column, the more contact/friction in the bore with the faint, invisible reaming marks and the more likely the wad will rotate around it's axis - if it's tightly holding a ball!

For smokeless powder, Alcan's AL8 and Herculese Blue Dot worked well in my 10 bore double for high speed shot loads with 2 ounces of shot.

Just a thought.