No, I was not aware of that. But I am aware of the fact that #4's seem to have no problem killing ducks. I was on a goose hunt last year and we found we had as many ducks as geese coming into our decoys. I wasn't expecting this so all I had was BB's for geese. I borrowed a few rounds of #4 steel (Federals I beleive) off a fellow hunter dropped three ducks dead with three shots. While three ducks may not be a good "big picture" indicator of how well they perform, the guy I borrowed them from uses them exclusively. He hunts A LOT more ducks than I do so I have to take his word for it that they work. Personally i normally use #2 steel for ducks and I will continue to do so because it works but I have no qualms about using #4's if I had to.You are aware of the fact that #4s do not cary an ED of 235ft lb/in2 past 25 yards when shot at only 1300fps
You can do all the ballistics math you want but in the end the proof is in the freezer.