The Migratory Bird Act requires all bird hunting with shotguns to a maximum of 3 rounds in the gun at all times in the field. This is true for pumps and semi autos.
The Saiga 12 shotgun comes standard with a 5 rd magazine from the factory and some that have the factory LRBHO come with a 4 round mag.
Izhmash also makes an 8 rd and a 2rd mag but these are rare items to find in the US. I have a couple of the original 2 rd hunting mags as well as others I've made myself from cut down and plastic welded 5rd mags. I used to make and sell these.
It isn't worth the expense or the trouble whe