Here is a link to a product page. Only problem is that it would probably cost more than your house before they add shipping.
http://www.savagerangesystems.com/bullettraps/
I like the 55 gallon barrel idea. Put 3" of sand in the bottom, fill it with water, and cut a 6" hole in the top. Then, consider the noise you will be making, and the proximity of your neighbors.
A more practical solution may be your nearest forest, woods, back roads, desert. I have done this and popped a round or two into sand, or mud. You can even recover the slugs fairly easily.