I read the same article that was referenced above (though I think the poster had a little trouble with his html).
The proper link is:
www.firearmstactical.com/briefs10.htmI read the same article a few years back, and chose the Federal F127 #1 buck in 2 3/4". Here are the operative paragraphs:
12 Gauge Shotshell AmmunitionFor personal defense and law enforcement applications, the International Wound Ballistics Association advocates number 1 buckshot as being superior to all other buckshot sizes.
Number 1 buck is the smallest diameter shot that reliably and consistently penetrates more than 12 inches of standard ordnance gelatin when fired at typical shotgun engagement distances. A standard 2 ¾-inch 12 gauge shotshell contains 16 pellets of #1 buck. The total combined cross sectional area of the 16 pellets is 1.13 square inches. Compared to the total combined cross sectional area of the nine pellets in a standard #00 (double-aught) buck shotshell (0.77 square inches), the # 1 buck shotshell has the capacity to produce over 30 percent more potentially effective wound trauma.
In all shotshell loads, number 1 buckshot produces more potentially effective wound trauma than either #00 or #000 buck. In addition, number 1 buck is less likely to over-penetrate and exit an attacker's body.
For home defense applications a standard velocity 2 ¾-inch #1 buck shotshell (16 pellet payload) from Federal, Remington or Winchester is your best choice. We feel the Federal Classic 2 ¾-inch #1 buck load (F127) is slightly better than the same loads offered by Remington and Winchester. The Federal shotshell uses both a plastic shot cup and granulated plastic shot buffer to minimize post-ignition pellet deformation, whereas the Remington and Winchester loads do not.