For that reason and others I no longer pick up brass other than my own. If brass is on the ground it's due to the prior shooter not a reloader, a reloader who knows that brass is past use or someone too lazy to police the area.
I don't care to figure out which is which and leave it there. We shoot at private ranges where they do a brass sweep 1-3x a month for scrap, putting that $$ back in to the general range fund.