[Yohan]

What exactly is the gauge measuring? And why is a small gauge considered to more powerful than a bigger gauge? Inquiring mind wishes to know.

[Badger Arms]

IIRC, Gauge is the size of the round lead ball that will fit down the bore. A ball that weighs one pound will give you a 1 gauge barrel. When two balls equal a pound, the diamater of the balls is 2 gauge. Therefore, 2 gauge is 1/2 a pound. 12ga is then 1/12th of a pound. 16ga is 1/16th of a pound (1 ounce round ball). There are a few variances, but they simply measure bore diameter such as .410 inches and 9mm which are both shotgun shell names.

[BigG]

Badger is correct. The practice of calling out sizes in caliber (1/100 of an inch) is relatively recent. In the Kentucky rifle days a gun was calibrated at so many balls to the pound. In that case, the larger the number, the smaller the caliber. Shotgun gauge is similar.