BB for ducks? I used 5's and 6's mostly - & 4's for long range pass shooting.
I did try 12 guage 1 1/4oz. 7 1/2's for ducks over decoys with open choke after reading an article in gun mag by Peter Capstick. That worked very well, surprisingly, with head and neck hits killing the ducks cleanly, with non in the breast meat.