My late friend Will, used 2 ounces 7 1/2's from a 6 (5) bore Westley Richards SXS. Very heavy gun with huge breeches and 36" tubes. It had a block with a silver line for sighting with ball, I assume.

Will had it re-furbished by H&H back in the 70's and they reamed the tube to 5 bore, for a smooth finish. It really shot well and used to powder the birds if you could get it swinging fast enough to catch up then slap the trigger when the bead 'just' passed the bird. Catch up it did and you could not stop and shoot behind the bird if you tried deliberately. It had automatic lead, built-in- about 14 pounds IIRC.