I've never hunted ducks, but I use hex blunts for grouse. Ruffed grouse are amazingly tough critters, but a hex to the chest puts their lights out reasonably fast.
For home-made, I've wondered about using chisel-shaped stone or metal heads. One of the TBB volumes talks about them. Seems like they'd be easy to make, fairly hard to lose, and would probably do the job.