Shotgun ammunition is measured in gauge rather than in caliber. Because shotguns are very versatile firearms, ammunition for them comes in a very wide variety of types, sizes and power. The gauge number is on the shotgun ammunition box. Your shotgun ammunition much match the gauge of your shotgun.
The term “gauge” describes bore diameter. Unlike “caliber” used for handguns and rifles, the larger the number, the smaller the bore. The “bore” is the inside diameter of the barrel. So a higher gauge number means the internal diameter of the barrel is smaller. A smaller gauge number means the internal diameter of the barrel is bigger. Therefore, a 12-gauge bore is bigger than a 20-gauge bore. Gauge measures shotgun ammunition as well, rather than in caliber for handguns and rifles.
Gauge defines the number of solid balls the same diameter as the inside of the barrel that could be made from a pound of lead. Thus, the 10-gauge shotgun is larger than the 12-gauge, which is larger than the 20-gauge. While there are many different sizes, or gauges, of shotguns, most recommend 12 gauge and 20 gauge shotgun for home defense.
The length of the shell is another very important number. Not all lengths will feed in all shotguns. The common lengths are 2-3/4 inches, 3 inches, and 3-1/2 inches. The longer the shell, the more shot pellets and powder it can contain. Ne ver use a shotgun designed to load a shorter shell to fire a larger shell, even if the larger shell physically fits within the gun. This can be extremely dangerous as the gun may not be able to handle the higher pressures a more powerful ammunition produces.
Shotgun Ammunition Shell Type
There are three basic types of shells:
- High brass shells are shells that have a brass base which extends up the shell body by about three-quarters of an inch.
- A relatively narrow band of metal around the base of the shell characterizes low brass shells. Low brass ammunition is generally less powerful than high brass.
- Active shells are formed entirely of plastic, except for a miniature metal button which holds the primer in the center of the case head. Active shells are useful for hunters and others whose ammunition might get wet in the field, because they are nearly impervious to rust.
Dram Equivalent (power)
Dram Equivalent will tell you how powerful the ammunition is. Originally, drams were a black powder weight measure, but now modern shotgun ammunition uses smokeless powder. Shotgun ammunition manufacturers use dram equivalents to indicate how much power the load has. The higher the dram equivalent number, the more energy the ammunition has and the faster the shot will travel.
Shotgun ammunition falls into three general categories:
BIRDSHOT – Shotgun ammunition which uses very small pellets with individual projectiles of less than .24″ in diameter that discharge in quantity from the shotgun. The size of the shot is given as a number or letter–with the larger number the smaller the shot size. The name comes from the shell’s common use, bird hunting. The finest size generally used is #9 which is approximately .08″ in diameter and the largest common size is #2 which is approximately .15″
BUCKSHOT – A type of shotgun ammunition that uses medium-sized to large-sized pellets of .24″ in diameter or greater, that discharges in quantity from a shotgun. Generally the larger the pellets, the fewer of them in the casing.
SHOTGUN SLUG – An individual cylindrical projectile that discharges from a shotgun. As a single projectile, slugs must be carefully aimed to be effective.
Buckshot is generally recommended for home defense. The larger the buckshot the greater the stopping power and the greater the chances of over-penetration and injury to innocents in other rooms or buildings. If you are in a densely populated home or neighborhood you can minimize the risk of over-penetration by using small game loads of #6 Birdshot or smaller, but this sacrifices a great deal of effectiveness. Versatility in available loadings is a great strength of shotguns, but you must choose your loads carefully for your environment.