It depends on a few things such as how fast the bird is traveling, how far away it is, what style choke you are using and even the strength of shells you are using (how quickly the shot travels). I would suggest practicing with sporting clays. It's a lot of fun and you will get the practice needed to understand how much to lead a bird in different situations.
If you don't mind spending in the neighborhood of $800-$1,000 for a good used gun I would definitely recommend trying the Benelli Sport (12 gauge auto.). This is a great gun for sporting clays and waterfowl. The regular sport is no longer made so if you are looking for one that is brand new the Sport II model is now it’s replacement. I have not shot the second version but if it’s as good as the first or better then it’s worth every penny. It looks a little nicer also. Your best bet is to shoot several models before making up your mind. My main reason for liking this model so well is it f