Finally got out to shoot, only loaded 4 for initial test.
8 Drams of Swiss 1 1/2, Fed 215 primer, nitro card and SPG lubed fibre wad, overshot card wad under 875 grain Paradox bullet from vintage H&H mould sized to bore diameter.

25 yards today, standing rest, crossing a bit but can work on that. R1/L1 are 1 1/4", better hold for R2/L2 out of dirty barrels were 5/8"
The 2 "smaller"

uppermost holes are from a .577BPE…..

I'm a happy camper. Recoil about as expected, close but not quite as much as my 8 bore GE Lewis with 10 Dram & round ball.
- Mike