I would suggest trying to shoot geese with a non-choked 20 bore might be more than challenging.
Shooting ducks over decoys, would work quite well, I would think, as long as there was some load
development to get a decent load. Shooting should be 30yards and closer, so workable.
Geese, if drawn in close, NP, but with limited # of the heavier shot in a wide load, might work, but?
?
This is all speculation as I have not gone that route. I quit hunting migratory birds when the lead-shot
ban was brought out.