Ok... so I realize this is somewhat pointless in terms of effectiveness. But I had to try it. #00 Buckshot.
Easiest stuff to powdercoat EVER. Just toss them in a tub with a spoon of Smoke's PC powder and swirl them around - no need for airsoft BB's, they tumble coat perfectly well on their own.
This should make an acceptable 'Merica load for a friend's 4"-bore cannon on the 4th!!