Check out the Tri-Ball load from the Dixie Slug Company. It has three balls that are .600" diameter and weigh 320 grains each, the 3" load packs 2580 foot pounds of energy and they're designed so most guns will throw a pattern that'll keep all three pellets on a deer out past 50 yards. That's like hitting a deer with three 20 gauge slugs simultaneously.
http://www.dixieslugs.com/products.html
Here's a comparison of the tri-ball load versus 00 buck. Look at the single pellet energy figures and you'll see that at 60 yards the tri-ball pellets have over 3.5 times the energy that a 00 buck pellet has at the muzzle.
http://www.dixieslugs.com/tball2vs.htm