John:
Not sure what size bismuth shot is normally available on those shoots.
In the Top End I use Bi fours for ducks and twos for magpie geese.

I could have taken Bismuth fours to Victoria with the Rigby but all my cartridges are home-loaded with plastic wads.
The laugh is, normal plastic wads are rapidly bio-degradable here in the monsoon tropics through dry-season grass fires, extreme temperatures and high UV ratings!