The steel shot that I found to be most effective for ducks is Hevi Metal. My son and I both use 3" # 3 and 3.5" is also very good but 3" is plenty. The next best shell that I have had great success with is Black Cloud 3" # 3. This also works very good. It is available in 2 load sizes. High velocity 1 1/8 oz, travels at 1635 FPS, the other load is 1 1/4 oz, travels at 1450 FPS. It cost less than Hevi Metal but does require more follow up shots to finish off the duck.