I used that same load AA cases red Win wad 1 3/8 copper plated 5s with 571 on ducks. Guiding one day I pass shot many ducks(Pintails). Party couldn't hit the darn things. 10 point ducks and we could have shot 70 total. Only 30-35 yard shots. You could also use 27 1/2_grains of Alcan 7 too...loaded number 3 shot for Canada geese with either powder
When I was younger, about 16, a older hunting friend showed me what a 2 3/4", "Short Mag" loaded with #4 lead pellets could do.
He waited for a mallard to come straight over us and estimated about 16 feet and pulled the trigger.
After a small wait, we saw the bird that was 70 yards above us, fold up and start falling.
A few years later, w571 and Blue Dot were helping me bag a limit of ducks, with no problems.
The only problem was that some of those 70 yard birds that fell dead and not spinning with a broken wing or slowing down some how,
if they hit the water, breast first, would sometimes split the skin
and have to be breasted, instead of picked, for the BBQ, with the skin on.
Plus lead pellets were a lot easier on your teeth, than steel pellets !!