I take it the RB groups dirverging or crossing along with elevation -ie: the three together, then spearation and 3 more together are the individual barrel groups?

When I shot my double using the SR4756 powder, I use an undersized ball with a plastic cup wad underneath to hold it centred in the barrel. With the heaviest loads, the barerls shot together, same elvation. I might have been just lucky.

My .58 muzzleloading double rifle shoots to diffferent elevations right and left with too little or too much powder. They cross with 80gr. BP, right bl. 1 1/2" higher and to the left, then come together at the same elevation, same hole group with another 20 gr. of BP, then spearate perfectly with another 10gr. (110) BP (1" apart, same hole), then they diverge 2" apart with another 10gr.(120) with the left shooting higher by 1 1/2" than the right.

I found smaller balls did not shoot the same as larger diameter balls - so all this means is that any change, even wads, can change the regulation and grouping of the barrels - which is exactly what Ross Seyfreid found with his double guns. This is what makes Double Gun shooting so much fun, even though it is frustrating MOST if the time.

From the appearance of the RB groups, I'd be trying 33gr.