I would think there is far more natural lead in the environment than gets spread around by firearms. You will get a concentration in gun clubs of course certainly at trap and sporting clays ranges but that is a contained area and has nothing to do with hunting. This is just another way to get rid of firearms. The irony is it will retire many old fixed choke guns and cause the manufacture and sale of new guns which can shoot steel.
as for rifles ammo manufacturers will convert to copper and other non toxics. It won't make people quit hunting which is the real intent. Trudough is pizzzing off more people every week. This will mobilize more people "against him" than win some over.