It's about gun control and I believe it has nothing to do with the enviroment.
Banning lead bullets is simply a way to raise ammo prices. If guns can't be banned, the anti crowd can still put up barriers to firearms by attacking the ammo.
Making ammo harder to get through fingerprinting or requiring permits to buy or simply making ammo more expensive by banning a common material will limit those with working firearms.
Call me paranoid, but I think the Brady group is smart enough to realize by banning ammo, they in turn ban guns. Being "green" is just another way to do it.
"He who laughs last, laughs dead." Homer Simpson