Shotgun ammunition is measured in gauge rather than in caliber, and the gauge number can be found on the shotgun ammunition box. Because shotguns are such versatile guns, their ammo comes in a wide variety of types and varying sizes and power.
Gauge describes bore diameter or the inside diameter of the barrel. Unlike caliber, a term used for handguns and rifles, the larger the gauge number, the smaller the bore diameter. So a smaller diameter barrel correlates with a bigger gauge, and a bigger barrel diameter correlates with a smaller gauge. For example, a 10 gauge shotgun is bigger than a 12 gauge, which is bigger than the 20-gauge.
Another very important number is the length of the shell. The common lengths are 2-3/4 inches, 3 inches, and 3-1/2 inches. Longer shells contain more shot pellets and powder than shorter ones. Each shotgun model is designed to shoot specific lengths, and they should not be used to fire larger shells. It doesn’t matter whether the shell fits into the gun or not, if the shell is too long, the gun may not be able to handle the higher pressures that longer ammo would produce, and this can be very dangerous.
There are three basic types of shotgun ammo. High brass shells have a brass base extending up the shell’s body, while low brass shells have a relatively narrow band of metal just around the base of the shell. Low brass ammo is usually not as powerful as high brass. Active shells are made fully of plastic, with a small metal button which holds the primer in the center of the case head.
Another way of categorizing shells is as birdshot, buckshot, and shotgun slug. Birdshot is a form of ammunition that uses very small pellets with individual projectiles. These projectiles are less than .24″ in diameter. The larger the number (size) of these shells, the smaller the shot size. It’s most often used for hunting birds, which is how it got its name. Sizes can vary between .08″ in diameter and the largest common size, which is approximately .15″. The buckshot uses medium-sized to large-sized pellets of .24″ in diameter, or greater. The bigger these pellets are, the fewer of them inside the shell. Last but not least, the shotgun slug. This one is an individual cylindrical projectile. These projectiles must be carefully aimed in order to be effective.
Depending on what kind of shotgun you own, you will need a certain size of ammo. Always use the right gauge for the shotgun you have, and never a larger one. You can find all types of shotgun ammo for sale online or in stores.