I use the same olive oil soaked felt wads in a Pedersoli 20 gauge SxS that I use in rifled bore loads. I try to keep things simple.
60 grains of Swiss 3f, card, 1/2 wad, load (.60 ball in right, 1 ounce shot load in the left), other half wad.
Keeps the ball on a 12 x 12 steel plate at 50 yards offhand and makes a mess of a milk jug at 25 yards. Ymmv.
wm