California Firearms Safety Certificates (CAFSC) 2025 – 400 Free Practice Questions to Pass the Exam

Shotgun shells are generally measured using the gauge system, which indicates the internal diameter of the shotgun barrel. This measurement is derived from the number of spherical lead balls that fit the diameter of the barrel in a pound; for example, a 12-gauge shotgun has a bore diameter such that 12 lead balls of that diameter weigh one pound. The gauge measurement is unique to shotguns, unlike rifle and handgun ammunition, which is typically measured in caliber (diameter in inches or millimeters).

While other measurement units like millimeters can be used for specific shotgun rounds (particularly in the case of metric systems), gauge remains the standard and more widely recognized method for categorizing shotguns. This means that when selecting shotgun shells or considering shotgun specifications, gauge is the primary measurement to focus on, making it essential for understanding shotgun types and compatibility.