Canadian Firearms Safety Course (CFSC) Practice Exam

Shotgun barrels are measured by gauge, which is a unique system used specifically for shotguns. The gauge of a shotgun refers to the number of lead balls of a certain diameter that would weigh one pound. For example, a 12-gauge shotgun means that twelve lead balls of the same diameter as the inside of the barrel would weigh one pound. This measurement system is distinct from caliber, which typically applies to rifles and handguns, and is usually expressed in inches or millimeters.

In contrast, inches and millimeters are used more commonly for measuring the bore size of rifles and handguns. Caliber refers to the diameter of the bullet used in a firearm, which is not applicable to shotguns in the same way. Therefore, gauge is the correct measurement system used for shotguns, reflecting the unique characteristics of how they are built and how they fire.