Ammunition
The extremely large caliber of shotgun shells has led to a wide variety of different ammunition.
Shotshells are the most commonly used round, filled with lead or lead substitute pellets.
Of this general class, the most common subset is birdshot, which uses a large number (from dozens to hundreds) of small pellets, meant to create a wide "kill spread" to hunt birds in flight. Shot shells are described by the size and number of the pellets within, and numbered in reverse order (the smaller the number, the bigger the pellet size, similar to bore gauge). Size nine (#9) shot is the smallest size normally used for hunting and is used on small upland game birds such as dove and quail. Larger sizes are used for hunting larger upland game birds and waterfowl.
Buckshot is similar to but larger than birdshot, and was originally designed for hunting larger game, such as deer (hence the name). While the advent of new, more accurate slug technologies is making buckshot less attractive for hunting, it is still the most common choice for police, military, and home defense uses. Like birdshot, buckshot is described by pellet size, with larger numbers indicating smaller shot. From the smallest to the largest, buckshot sizes are: #4, (called "number four"), #1, 0 ("one-ought"), 00 ("double-ought"), 000 ("triple-ought") and 0000 ("four-ought"). A typical round for defensive use would be a 12 gauge 23⁄4" (7 cm) length 00 buck shell, which contains 9 pellets roughly 8.4 mm (.33 inch) in diameter, each comparable to a .38 Special bullet in damage potential. New "tactical" buckshot rounds, designed specifically for defensive use, use slightly fewer shot at lower velocity to reduce recoil and increase controllability of the shotgun. There are some shotgun rounds designed specifically for police use that shoot effectively from 50 yards (46 m) with a 20" diameter grouping of the balls.
Slug rounds are rounds that fire a single solid slug. They are used for hunting large game, and in certain military and law enforcement applications. Modern slugs are moderately accurate, especially when fired from special rifled slug barrels. They are often used in "shotgun-only" hunting zones near inhabited areas, where rifles are prohibited due to their greater range.
Sabots are a common type of slug round. While some slugs are exactly that—a 12-gauge metal projectile in a cartridge—a sabot is a smaller but more aerodynamic projectile surrounded by a "shoe" of some other material. This "sabot" jacket seals the barrel, increasing pressure and acceleration, while also inducing spin on the projectile in a rifled barrel. Once the projectile clears the barrel, the sabot material falls away, leaving an unmarked, aerodynamic bullet to continue toward the target. The advantages over a traditional slug are increased shot power, increased bullet velocity due to the lighter-mass bullet, and increased accuracy due to the velocity and the reduction in deformation of the slug itself. Disadvantages versus a traditional slug include lower muzzle momentum due to reduced mass, reduced damage due to smaller bullet diameter, and significantly higher per-unit cost.
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