RST copper plated lead shot is illegal for hunting waterfowl. Plated lead shot hardens the pellet, less shot deformation, and better patterns. Plated shot is good for turkey, pigeon, pheasant, etc.
You need to use either steel, bismuth, tungsten. Go here to this link.
http://www.fws.gov/birds/bird-enthus...g/nontoxic.php
People in this forum have used Kent's Tungsten-Matrix which is safe for older doubles. I thought Rio had a non steel waterfowl ammo but I can't find it.
Google Kent's Tungsten-Matrix and you will get hits on who sells it and you can have shipped to you.