My second gun was a 870 pump. Good gun. If you're shooting lead go with #4 shot and full chock. If you're shooting steel go with #2 and modified chock. It's not recommended to use full chock with steel shot.I've been hunting for years and have been using #4 lead until we had to change to steel shot. #4 has very good penetration for ducks or geese.
good luck hunting.