I go to place where people shoot into a bank when I go shooting. On a whim, I took my 2'X4' gold classifing screen (it's a wooden frame with 1/2" mesh stapled to the bottom) and a shovel and scooped up the sandy soil where the bullets impact. In six scoops I had about 20 lbs. of spent bullets. I figure if I stay there for a while, I could quickly get half a ton or so. Be sure to wear a mask if you do this, don't want to breath in any lead dust from the ground.