In his book The Zombie Survival Guide, Max Brooks is dismissive of the shotgun as an anti-zombie weapon due to its “bulky” and “burdensome” shells. While Brooks does acknowledge the lethality of a twelve gauge, he seems to miss its virtue of increased hit probability against head-sized targets.
If you are shooting at a zombie with a single projectile, your point of aim will have to fall within the 6-inch circle corresponding to the frontal area of his brain (the average human brain is about 6 inches wide extending from the top of the head to just below the nose). That’s a small target to hit, especially when you consider that it will be jerking and swaying as a result of the zombie’s uneven gait. Exacerbating the problem is the fact that you will be in a horrifying situation, which will likely induce a massive adrenaline dump (and perhaps another type of dump as well). With your heart rate soaring over 150 BPM, your fine motor skills won’t be what they were at the practice range.
Let’s take a look at some geometry to see how a shotgun can help:
Circle A is the 6-inch circle corresponding to the location of the brain. Its radius is 3 inches and area just over 28 square inches.
Circle B represents the 10-inch spread of a 00 buckshot round at a range of ten yards. As you can see, the shooter’s point of aim can be outside the “brain circle” by as much as five inches (the circle's radius) and still result in a lethal pellet strike.
Circle C is the lethal area of aim with the shotgun at a range of ten yards. The circle’s radius is 8 inches (the radii of Circles A and B combined) giving it an area of over 200 square inches.
So the lethal area of aim when firing 00 buckshot at this range is over 600% greater than it would be with a single projectile (200 sq. in. versus 28 sq. in.). That is a much-needed margin for error in a deadly situation. Keep in mind that the math here is rough. The pellet spread obviously doesn’t reach every edge of Circle B, meaning that borderline shots on other vectors could still result in a miss. Also note that at greater ranges, the spread will be such that all pellets may miss the brain area even on a perfectly aimed shot.
Pat Kilbane is best know for his three-year run on Fox's Mad TV, though many remember him as "the anti-Kramer" in the Seinfeld episode "The Bizarro Jerry." Also a writer, Pat spent two years under contract with Dreamworks developing science-fiction concepts for television, and recently authored The Brain Eater's Bible, a zombie field manual available in hardcover from Amazon and as an iPad app from the iTunes Store.