Hay there Im from England so not sure what our shot sizes would be over the big duck pond.

number 4s steel for very close ducks(flighting them onto ponds ect) prefrably no more than 20yds!!

Number 4s Bismuth if you have it over there. Its all I use and have droped everything from teal springing of a pond, high phesants and most impresive of all a mallard flying like a bat out of hell at over 70yds!!!!!!! They kill beter than scuds.

Tungsten. size 3s and 1s are nice on very tough birds but at closer ranges it gives a very tight pattern!!!!