I think this is the answer
http://www.polywad.com/spredr.html but the blunderbuss is also a good idea. While you are there take a look at the Polywad's Quik-Shok Sabot Slugs they sell. They toss a 1 1/8 ounce slug down range and it is designed to frag onto 3 pieces. That is more lead weight than is on any one of my tires! I'll look forward to checking out your new Toy Tuesday evening.