At close range bird shot can be deadly. At 9-10 feet in most guns it has only spread to about 1 1/2 to 2 inches and makes quite a mess...penetration is low in #7 or #8 but obviously is much greater as the mass of the individual pellet increases...ie #4 birdshot.
http://www.firearmsid.com/A_distshotpatt.htm
http://www.thetruthaboutguns.com/2010/02/robert-farago/shotgun-penetration-with-various-rounds/
Thanks, the gelatin block shots are very graphic and easy to understand.
http://www.thetruthaboutguns.com/2010/02/robert-farago/shotgun-penetration-with-various-rounds/