Video of me shooting my 8 Bore GE Lewis is on the forums somewhere, can’t find it at the moment.
10 Drams of Swiss 1 1/2 and a .875 round ball. 1 card wad over powder then SPG soaked fibre filler wads under the ball to bring it up to proper height in the case neck.
Very acceptable 2 1/2” right/left accuracy at 25 yards with that obligatory cloud of smoke.

My shots were offhand, but like Daryl I’d suggest padding the sticks then resting your left hand on the pad rather than the bare fore end on the sticks.
………..However, your milage may vary.

BTW: you handle the recoil quite nicely. No drama. No barrels pointing up to the sky like some.
- Mike