to the original poster...keep shooting...there are fewer BB's in a shell than 8's, so there is more change for a small clay to fly through a pattern unscathed (that is what Swampcollie was getting at).... I agree with the advice to start out with 2's or 3's and an IC choke...the most common equipment mistake I used to see when guiding was people shooting too much choke for decoying birds...if you go tighter than Modified you need to be a VERY good shot to realize any benefit.... if you go too tight your patterns will blow out and you risk damaging your gun (this is why factory full is not marked for steel shot generally).... this is a ways down the road, but while you're practicing, once you have one type of lead down practice the others as well, it is a good idea to be able to shoot pull-through, pull-away, and sustained lead because they will help you on shots from certain angles....
ORIGINAL: dukbuster
I would say go with 4's and a modified choke, because a modified will give you slightly more range while still being open enough for the close in shots.
And the reason for the fours is, when guys hunt pheasants(which in most cases are bigger than ducks) they use 5's 6's or 7's...all smaller shot than fours on a bird bigger than a duck.
dukbuster...just one question...what kinds of ducks are you shooting, teal and spoonbills only? while a pheasant had more feathers than a duck their actual body is definitely not bigger than a typical puddle duck....