2 1/4 drams or more should get the job done. I used this load in a 14 bore for years and it worked on ducks, with a somewhat heavier charge of lead. (1 1/4 Oz.)
Have a double 19 bore flint, and it liked 2 1/2 drams though, and 1 1/4 Oz . Worked very well with that load.
Try on paper for pattern, then tin cans. 5 or 6 hits on a bean can at 40 yards would be good.