I've played around with these loads, GoodCheer. Using my 20 ga. cylinder bore I monkeyed with ball-plus-swan shot loads using .295" lead balls I cast for my .30 caliber rifle. I started out using my standard loading, powder, hard card, cushion wad, patched roundball, swan shot and then overshot card. I tried it with 3 swan, and 7 swan, results were poor. I then tried it with the same wadding but with bare ball +3 swan or 7 swan, same poor results. Not much better using just swan shot, either 6 or 12. I then switched wadding, used tow, and loaded roundball +3 swan and +7 swan, got better but still unimpressive results. I tried the same thing using cedar bark wadding, same results.
I was about to give up on it when I decided to try putting the swan shot down first, then the ball. I was pretty surprised. Using either my modern hard card + cushion wad or tow, I got very much better results. I tried cedar bark, same thing. Some of the shots put the ball well into the black with the 3 swan shot almost touching it, pretty impressive. I had my best luck with tow, by far, but the very best I could do was with tow, swan shot, ball, tow, in that order. All the tests were done in the 20-25 yard range, offhand.
This first target shows two shots. Shot #3, ball+6 swan over, the ball is a bullseye on the 1" black, but only 2 swan are on the paper. Shot #2 shows 3 swan loaded first, then ball, all grouped near the 1" black.
Second target again shows two shots, loaded the same except #1 with 3 swan over the ball, #2 with 3 swan under the ball. The two balls are in one hole, but look at the improvement when the swan are loaded under the ball.
And, I found results shooting just swan were inconsistent, but not all shots were unusable. This one with 12 swan, tow wadding, all 12 on the paper and grouped well. 1" bull. I think tow is the secret, but this needs more work.
BTW, I chose to load either 3 or 7 swan shot with the ball because I've found original sources stating that was done in the day.
Spence