Shotgun Shell - Shotshell Sizes

Shotshell Sizes

Shotgun shells are generally measured by "gauge", though in Britain and some other locations outside the United States the term "bore" is used with the same meaning. Rifles and handguns are almost always measured in "caliber", which is simply a measurement of the internal diameter of the barrel measured in millimeters or inches and, consequently, is approximately equal to the diameter of the projectile that is fired. By contrast, shotguns are usually measured by "gauge", which is the weight, in fractions of a pound, of a pure lead round ball that is the same diameter as the internal diameter of the barrel.

For example, a shotgun is called 12-gauge because a lead sphere that just fits the inside diameter of the barrel weighs ⅟12 of a pound. This measurement comes from the time when early cannons were designated in a similar manner—a "12 pounder" would be a cannon that fired a 12 pound (5.5 kg) cannonball; inversely, an individual "12-gauge" shot would in fact be a ⅟12 pounder (38 g). Thus, a 10-gauge shotgun has a larger-diameter barrel than a 12-gauge shotgun, which has a larger-diameter barrel than a 20-gauge shotgun, and so forth.

No.of lead balls in one pound diameter of the requisite pure lead ball
10 0.78" (19.7 mm)
12 0.73" (18.5 mm)
16 0.66" (16.8 mm)
20 0.62" (15.6 mm)
28 0.55" (14.0 mm)

The most popular shotgun gauge by far is 12-gauge. The larger 10-gauge, once popular for hunting larger birds such as goose and turkey, is in the decline with the advent of longer, "magnum" 12-gauge shells, which offer similar performance. The mid-size 20-gauge is also a very popular chambering for smaller-framed shooters who favor its reduced recoil, those hunting smaller game, and experienced trap and skeet shooters who like the additional challenge of hitting their targets with a smaller shot charge. Other less-common, but commercially available gauges are 16 and 28. There are also some shotguns measured by diameter, rather than gauge. These are the .410 (10 mm), .380 (9 mm), and .22 (5.5 mm); these are correctly called ".410 bore", not ".410-gauge".

The .410 bore is the smallest shotgun size which is widely available commercially. In the UK, 9 mm shotguns are quite common for use in "GardenGuns" and folding shotguns. For size comparison purposes, the .410, when measured by gauge, would be around 67- or 68-gauge (it is 67.62-gauge), The .410 is often mistakenly assigned 36-gauge. The 36 gauge was in fact a .360 diameter cartridge which was 1.5" in length and is now obsolete. They are not the same cartridge at all.

Shotshells are also available in common handgun calibers, including as .38 Special and .44 Magnum; these are often used in revolvers for defense against snakes at very close ranges, or for killing small pests such as rats. A number of single shot pistols and rifles are made in .45 Colt with special screw-in chokes allowing the use of .410 shells—usually the chokes are designed with deep grooves parallel to the bore designed to stop the spin of the shot column, as the .45 Colt barrel is rifled. Taurus sells a model called The Judge, which accommodates both .45 Colt and .410 shotshells. Recently, S&W came out with a revolver dubbed the "Governor," which not only shoots .45 Colt and .410 shotshells but also .45 ACP with the aid of moon clips.

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