What size cartridge do you use for pigeon shooting?

PIGEON SHOOTING
Peter Theobald
Generations of experience and testing has established beyond doubt that the most consistently effective combination for killing pigeons over decoys, is 30 gms (1.1/16oz) of No. 6 shot fired out of a 12-bore, and using no more than quarter choke.

People can argue until they are blue in the face that other combinations are more effective, but the fact remains that for average Joe Bloggs the one described here is their best bet.