Found these:
raditional Loads for Muzzle Loading Shotguns by Gauge.
Gauge
Amount of ffg powder
Amount of shot
20 gauge
2 ¼ drams = 62 grains
7/8 ounces
2 ¾ drams = 75 grains
1 ounce
In my 20 bore flinter with 31" bl. I use 3drams (82gr.) 2F and 1 1/8oz. shot.
I use a hard 1/8" card over the powder, then 1/2" cushion wad, then the shot, then the thin "B" was over the shot.
This load hammers clay birds. I swing past the bird and when the muzzle is about 1foot past, I slap the trigger. This passing of the bird, makes up for the slower ignition of the flintlock.
With a caplock, I slap the trigger when the muzzle touches the bird. This technique give perfect lead, every time.
Some guys use more powder and more shot than this.