Birdshot will absolutely kill a dude deader than Elvis...out to maybe 3-to-5 feet from the muzzle, depending on choke.
Putting birdshot in your splattergun turns it from a decisive fight-stopping implement of destruction into a glorified contact-distance bangstick.
People wind up using passed-down tales from Their Cousin, The Cop, who likes to talk about the time some beleaguered divorcee shot her vengeful ex- off the muzzle of a Citori with Winchester AA #7.5, as anecdata.