Effective January 1, 2010, the Oregon Department of Fish and Wildlife changed their guidelines for distance learning. Students are now required to spend a minimum amount of time on each course page before proceeding to the certification exam.

Click here to go to the latest version of the Today's Hunter in Oregon online course—the official hunter education course of the Oregon Department of Fish and Wildlife.

The following course material is for reference only. Please go to the new course to complete your Oregon certification.

A Shotgun's Gauge

Shotguns are classified by gauge, which is a measure related to the diameter of the smooth shotgun bore and the size of the shotshell designed for that bore. Shotgun gauge sizes

Common shotgun gauges are 10 gauge, 12 gauge, 16 gauge, 20 gauge, and 28 gauge. The smaller the gauge number, the larger the shotgun bore. Gauge is determined by the number of lead balls of size equal to the approximate diameter of the bore that it takes to weigh one pound. For example, it would take 12 lead balls with the same diameter as a 12-gauge shotgun bore to weigh one pound.
The .410-bore shotgun is the only exception to the gauge designation for shotguns. It has an actual bore diameter of 410/1000ths of an inch, which is approximately equivalent to a 67½ gauge.
Each gauge of shotgun shoots only shells of the same gauge. For example, 12-gauge guns use only in 12-gauge shells.
The gauge of a shotgun and the length of the chamber are usually marked on the rear of the barrel. The gauge of a shell and its length are marked on the shell as well as on the factory box.
If no chamber length is marked on the barrel, take the shotgun to a qualified gunsmith to have it measured.

Sizes shown are the minimum inside bore diameter with a tolerance of +0.020". Data is presented courtesy of SAAMI.