I had a .45 smoothbore some 4 or 5 decades ago. I would pour in 45gr 3F GOEX, then seat a 1/10" card wad on the powder. I'd then shove a .410 3" wad into the bore even with the muzzle, then fill it with #7 1/2 shot, then another wad over the top and seat that onto the over shot wad.
With this load, I broke 10 straight to win the trap shoot at our local rendezvous, shooting against 12's and one 10 bore SxS's. It is important to put a wad between the powder and a plastic shot cup.
For bunnies with that gun, I used a .433" rb with .020" patch and the same powder charge. Head shots to 50 yards was the norm.