One descriptor that has always puzzled me is the terminology for firearms. What exactly does a “twenty-two” mean? Although I think I know the meaning of the “9mm” for my Glock 19, why is a “thirty-aught-six” a common deer rifle? How about a “12-gauge” shotgun? This bothered me enough to require further exploration.
Caliber (or Calibre if you reside across the pond) originated in reference to the approximate diameter of the bullet used. Therefore a .22 (“twenty-two”) is approximately .22 inches in diameter. A Colt .45 has a bullet .45 inches in diameter (or a popular malt liquor beverage). Caliber can also be expressed in millimeters, for example, my Glock 19 has a bullet 9mm in diameter.
What about a .30-30? Or .30-06? .30-30 is still a commonly used cartridge and actually refers to the caliber (.30 inches) followed by the standard black powder charge in grains (30gr) in the days of early black-powder era cartridges when the convention was adopted. Modern .30-30 Winchester cartridge charge may differ from the original. “Thirty-aught-six” (.30-06) refers to caliber (.30 inches) with a modifier as to the year introduced (1906).
What about Shotguns?
For shotguns, ballistics are measured in a term related to caliber called gauge. Gauge refers to how many spheres of a given bore (inside diameter of the shotgun barrel) it would take to equal one pound. Therefore for a twelve-gauge shotgun it would take 12 spheres the size of its barrel’s bore to equal one pound. A “twenty-gauge” would take 20 spheres, reflecting its narrower bore. Interestingly, a .410 shotgun measurement is a caliber measurement. For shotshells, the size of the shot becomes a little more confusing in its naming convention. “Birdshot” are shells with pellets “poured” into the shell. “Buckshot” are much larger, such that may be used to hunt bigger game, hence the name. They are more carefully placed into the shotshell and packed with sawdust or tiny plastic pellets between them in order to control the spread as the shot strikes its target.
I measure roughly 46cm at my widest point (thankfully, my shoulders), so it would take at least a 460mm cannon to fire me.