A shotgun’s gauge, like a rifle caliber, is a measurement of its bore diameter. The way bore diameter is derived is odd, however. It is based on the number of balls that exactly fit the diameter of the bore that can be produced from one pound of lead. The number of balls from a 1-pound ball of lead that can fit into a 12-gauge diameter bore is 12. The only exception being the .410 shotgun that is measured instead in thousands of an inch.
Shotshells on the other hand are made up of a primer, shot, and powder. When a shotgun is fired, the firing pin strikes the primer, the primer ignites, firing the powder, which propels the shot. This is all usually contained in a plastic hull with a brass head, although paper and metal hulls do exist. Remington specifically uses a polyethylene plastic hull with a steel head coated with copper and brass.
The longer the shell and larger the gauge, the more shot pellets it can contain, while the higher the shot-size number, the more pellets a load will contain. Large, rifled slug shells can be comparable to .70 caliber bullets used for large game.
The size of the target and the range to it are the main factors that go into determining the shot load to use. For small game birds, such as dove or quail at shorter ranges, lead shotshells in 20 gauge or 12 gauge can be used with shot smaller than #6’s. 8-shot and 7 ½-shot work particularly well for dove.
For larger game birds such as ducks and geese, 12 gauge and 10 gauge loads with 3 ¼ drams of powder or greater are often used with large steel shot in #2’s or larger. These larger gauges can shoot magnum shells for long range, buckshot, or even one-ounce rifled slugs for big game. Smaller gauges carry proportionally smaller loads.
Shotgun Bore Diameters:
.410 bore – .410”
28 gauge – .550”
20 gauge – .615”
16 gauge – .670”
12 gauge – .730”
10 gauge – .775”