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Reader Question: I don’t understand how the gauge of a shotgun is determined. With rifles and pistols the caliber designation is frequently based on the diameter of the bore with the larger the number, the larger the caliber. But with shotguns, the reverse seems to be the case with the larger the number of the gauge, the smaller the bore diameter. What does the gauge designation mean and how is it determined?
—Ralph F., Bend, Oregon
Tom Tabor Answers: You are right…metallic cartridges are commonly named based on the diameter of the bullet they shoot. For example, a 6mm Remington rifle cartridge contains a bullet measuring 6mm in diameter and a .30-06 contains a bullet reflective of the first number in its name (.30 inches, or more precisely, .308 inches). Of course, not all cartridges possess a hyphenated name as in the .30-06, but in this case ’06’ relates to the year that that cartridge was developed (1906) and the .30 to the diameter of the bore.