I did see that just commenting on what I have seen people do
I have also seen people use a seive with holes drilled to about pellet size when they are picking up the shot I guess this would limit the bigger rocks but not the smaller pellet size
would a slopping chute with a slot cut into it work? my theory the shot pellet would roll and have enough inertia to jump the gap where as the stone might fall out? getting the slight width right might be trickie
even a step between chutes might work?