Shotgun cartridge
A shotgun cartridge, shotshell, or shell is a type of rimmed, cylindrical ammunition used specifically in shotguns. It is typically loaded with numerous small, spherical sub-projectiles called shot. Shotguns typically use a smoothbore barrel with a tapered constriction at the muzzle to regulate the extent of scattering.
Some cartridges contain a single solid projectile known as a slug. The casing usually consists of a paper or plastic tube with a metallic base containing the primer. The shot charge is typically contained by wadding inside the case. The caliber of the cartridge is known as its gauge.
The projectiles are traditionally made of lead, but other metals like steel, tungsten and bismuth are also used due to restrictions on lead, or for performance reasons such as achieving higher shot velocities by reducing the mass of the shot charge. Other unusual projectiles such as saboted flechettes, rubber balls, rock salt, and magnesium shards also exist. Cartridges can also be made with specialty non-lethal projectiles such as rubber and bean bag rounds.
Shotguns have an effective range of about with buckshot, with birdshot, with slugs, and well over with saboted slugs in rifled barrels.
Most shotgun cartridges are designed to be fired from a smoothbore barrel, as "shot" would be spread too wide by rifling. A rifled barrel will increase the accuracy of sabot slugs, but makes it unsuitable for firing shot, as it imparts a spin to the shot cup, causing the shot cluster to disperse. A rifled slug uses rifling on the slug itself so it can be used in a smoothbore shotgun.
History
Early shotgun cartridges used brass cases, not unlike pistol and rifle cartridge cases of the same era. These brass shotgun hulls or cases resembled large rifle cartridges, in terms of both the head and primer portions of the cartridge, as well as in their dimensions. Card wads, made of felt, leather, and cork, as well as paperboard, were all used at various times. Waterglass was commonly used to cement the top overshot wad into these brass casings. No roll crimp or fold crimp was used on these early brass cases, though roll crimps were eventually used by some manufacturers to hold the overshot wad in place securely. The primers on these early shotgun cartridges were identical to pistol primers of the same diameter.Starting in the late 1870s, paper hulls began replacing brass hulls. Paper hulls remained popular for nearly a century, until the early 1960s. These shotgun cartridges using paper hulls were nearly always roll crimped, although fold crimping also eventually became popular. The primers on these paper hull cartridges also changed from the pistol primers used on the early brass shotgun shells to a primer containing both the priming charge and an anvil, making the shotgun primer taller. Card wads, made of felt and cork, as well as paperboard, were all used at various times, gradually giving way to plastic over powder wads, with card wads, and, eventually, to all plastic wads. Starting from the early 1960s to the late 1970s, plastic hulls started replacing paper hulls for the majority of cartridges and by the early 1980s, plastic hulls had become universally adopted.
Typical construction
Modern shotgun cartridges typically consist of a plastic hull, with the base covered in a thin brass or plated steel covering. Paper cartridges used to be common and are still made, as are solid brass shells. Some companies have produced what appear to be all-plastic shells, although in these there is a small metal ring cast into the rim of the cartridge to provide strength. More powerful loads may use "high brass" shells, with the brass extended up further along the sides of the cartridge, while light loads will use "low brass" shells. The brass does not provide a significant amount of strength, but the difference in appearance gives shooters a way to quickly differentiate between high and low powered ammunition.The base of the cartridge is fairly thick to hold the large primer, which is longer than primers used for rifle and pistol ammunition. Modern smokeless powders are far more efficient than the original black powder, so little space is actually taken by propellant; shotguns use small quantities of double base powders, equivalent to quick-burning pistol powders, with up to 50% nitroglycerin. After the powder comes the wadding or wad. The primary purpose of a wad is to prevent the shot and powder from mixing, and to provide a seal that stops gas from blowing through the shot rather than propelling it. The wad design may also encompass a shock absorber and a cup that holds the shot together until it is out of the barrel.
A modern wad consists of three parts, the powder wad, the cushion, and the shot cup, which may be separate pieces or be one part. The powder wad acts as the gas seal, and is placed firmly over the powder; it may be a paper or plastic part. The cushion comes next, and it is designed to compress under pressure, to act as a shock absorber and minimize the deformation of the shot; it also serves to take up as much space as is needed between the powder wad and the shot. Cushions are almost universally made of plastic with crumple zones, although for game shooting in areas grazed by farm stock or wildlife biodegradable fiber wads are often preferred. The shot cup is the last part of the cartridge, and it serves to hold the shot together as it moves down the barrel. Shot cups have slits on the sides so that they peel open after leaving the barrel, allowing the shot to continue on in flight undisturbed. Shot cups, where used, are also almost universally plastic. The shot fills the shot cup, and the cartridge is then crimped, or rolled closed.
An atypical shotgun cartridge using rebated rims is the 12 Gauge RAS12, specially made for the RAS-12 semi automatic shotgun.
Sizes
Standard
Shotgun cartridges are generally measured by "gauge", which is theoretically based on the diameter of a lead ball whose mass is based on the gauge, but actually based on a UK law passed in 1885 which sticks reasonably closely to the theoretical definition. In Britain and some other locations outside the United States, the term "bore" is used with the same meaning. This contrasts with rifles and handguns, which are almost always measured in "caliber", a measurement of the internal diameter of the barrel in millimeters or inches and, consequently, is approximately equal to the diameter of the projectile that is fired.For example, a shotgun is called "12-gauge" because a lead sphere that just fits the inside diameter of the barrel allegedly weighs. 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 cannonball; inversely, an individual "12-gauge" shot would in fact be a pounder. 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.
The most popular shotgun gauge by far is 12-gauge. The bigger 10-gauge, once popular for hunting larger birds such as goose and turkey, is on the decline with the advent of the longer, "magnum" 12-gauge cartridges, 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. Several other gauges may be encountered, but are considered obsolete. The 4, 8, 24, and 32 gauge guns are collector items. There are also some shotguns measured by diameter, rather than gauge. These are the,, and ; these are correctly called ".410 bore", not ".410-gauge".
The.410 bore is the smallest shotgun size which is widely available commercially in the United States. For size comparison purposes, the.410, when measured by gauge, would be around 67- or 68-gauge. The.410 is often mistakenly assigned 36-gauge. The 36 gauge had a bore. Reloading components are still available.
Other calibers
Snake shot refers to handgun and rifle cartridges loaded with small lead shot. Snake shot is generally used for shooting at snakes, rodents, birds, and other pests at very close range. The most common snake shot cartridges are.22 Long Rifle,.22 Magnum,.38 Special, 9×19mm Luger,.40 Smith & Wesson,.44 Special,.45 ACP, and.45 Colt.Commonly used by hikers, backpackers and campers, snake shot is ideally suited for use in revolvers and derringers, chambered for.38 Special and.357 Magnum. Snake shot may not cycle properly in semi-automatic pistols. Rifles specifically made to fire.22 caliber snake shot are also commonly used by farmers for pest control inside of barns and sheds, as the snake shot will not shoot holes in the roof or walls, or more importantly injure livestock with a ricochet. They are also used for airport and warehouse pest control.
Shot shells have also been historically issued to soldiers, to be used in standard issue rifles. The.45-70 "Forager" round, which contained a thin wooden bullet filled with birdshot, was intended for hunting small game to supplement the soldiers' rations. This round in effect made the.45-70 rifle into a small gauge shotgun, capable of killing rabbits, ducks, and other small game.
During World War II, the United States military developed the.45 ACP M12 and M15 shot cartridges. They were issued to pilots, to be used as foraging ammunition in the event that they were shot down. While they were best used in the M1917 revolvers, the M15 cartridge would actually cycle the semi-automatic M1911 pistols action.