For close up over decoys you might be ok with #4 steel. However, I'd suggest #2 or #1, especially if these are fully plumed norther ducks. With norther mallards that migrate down from Canada through ND and western MN late season, I'll usually switch to BB's for big ducks and geese. They give more killing power out to 35-40 yards and penetration / ability to break wings on geese.