Shotgun shell

A 12 gauge shotgun shell in a transparent plastic hull, allowing the contents to be seen. From left to right: gunpowder, over-powder wad, shot wad, #8 birdshot, and over-shot wad

A shotgun shell (shotshell) is a self-contained cartridge loaded with lead shot or shotgun slug (or nonlead alternatives using materials such as steel, tungsten-nickel-iron, bismuth-tin, and tungsten-polymer) designed to be fired from a shotgun.

Most shotgun shells are designed to be fired from a smoothbore barrel, but with the recent gain in popularity of dedicated shotguns with rifled barrels for firing slugs, there are many rounds specifically designed to be fired from a rifled barrel. A rifled barrel will increase the accuracy of the shotgun with slugs, but makes it unsuitable for firing shot, as the rifling causes the shot to form a hollow "O" shape in flight.^[1] Some non-lethal shotgun ammunition is available in the form of slugs made of low-density material, such as rubber. See shotgun specialty ammunition for more information.

Construction of a typical shotshell

Modern shotgun cartridges typically consist of a plastic case, with the base covered in a thin brass covering. Paper shells 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 shell to provide strength. Often the more powerful loads will use "high brass" shells, with the brass extended up further along the sides of the shell, while light loads will use "low brass" shells. The brass does not actually provide a significant amount of strength, but the difference in appearance provides shooters with a way to quickly differentiate between high and low powered ammunition.

The base of the shotshell is fairly thick to hold the large shotgun primer, which is quite a bit longer than primers used for rifle and pistol ammunition. Modern smokeless powders are far more efficient than the original black powder used in shotgun shells, so very little space is actually taken by powder; shotguns use small quantities of powerful double base powders, equivalent to quick-burning pistol powders, with up to 50% nitroglycerin. After the powder comes the wadding. The primary purpose of a wad is to provide a gas seal, since without a wad the gas would just blow through the shot rather than propelling it. The 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 (known as obturation), 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 fibre wads are often preferred. The shot cup is the last part of the shell, 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 (which must be of the correct length to hold the desired quantity of shot), and the shotgun shell is then crimped, or rolled closed.

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.^[2] 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 1⁄12 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 1⁄12 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.

.22 Ratshot

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 (mathematically it is 67.62 gauge), not the sometimes mistakenly assigned 36 gauge.

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.^[3] 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.

Shotgun Gauge Diameter Formula

The standard definition of shotgun gauge assumes that a pure lead ball is used. With this assumption, since the room temperature density for lead is 11.34 g/cm³, and with there being 7,000 grains to a pound, the following formula results:

$d_n=\sqrt[3]{\frac{7000}{1501.339 \times n}}$

This formula accurately estimates the diameter (d_n) in inches of any shotgun gauge size (n). For example, a 67.62 gauge equates to a lead ball diameter of 0.410-inch by this formula, hence the .410 shotgun shell nomenclature.

Another source for a gauge diameter formula can be found in gauge (bore diameter).

Lead free shotshell

At the beginning of the 21st century lead-free shotshell ammunition loaded with steel, bismuth, or tungsten composite pellets instead of more traditional lead-based pellets was introduced.

Due to environmental regulations, hunters in Europe are required to use lead-loaded ammunition carefully. For instance, in France, they cannot fire in the vicinity of a pond. In fact, the laws are so complex that some hunters in Europe prefer not to risk getting into problems for firing lead pellets at wrong places, so they opt for composite pellets in all situations. The use of lead shot is also banned in Canada and the United States when hunting migratory game birds, such as ducks and geese, forcing the use of non-toxic shot in these countries for upland waterfowl hunting. (Lead shot can still legally be used in the United States for hunting game other than waterfowl. This means that manufacturers need to market new types of lead-free shotgun ammunition loaded with alternative pellets to meet environmental restrictions on the use of lead, as well as lead-based and cheaper shotshell ammunition, to remain competitive worldwide.)

The C.I.P. enforces approval of all ammunition a manufacturer or importer intends to sell in any of the (mainly European) C.I.P. member states. The ammunition manufacturing plants are obliged to test their products during production against the C.I.P. pressure specifications. A compliance report must be issued for each production lot and archived for later verification if needed.

Besides pressure testing, shotshells containing steel pellets require an additional Vickers hardness test. The hardness VH1 must be below 100 for the steel pellets used but, even so, steel is known to wear the barrel excessively over time if the steel pellet velocities become too high, leading to potentially harmful situations for the user. As a result, the measurement of pellet velocity is also an additional obligation for shotshells in 12, 16 and 20 gauges in both standard and high performance versions sold in Europe. The velocity of pellets must be below 425 m/s (1,390 ft/s), 390 m/s (1,300 ft/s) and 390 m/s (1,300 ft/s) respectively for the standard versions. Another disadvantage of steel pellets is their tendency to ricochet unpredictably after striking any hard surface. This poses a major hazard at indoor ranges or whenever metal targets or hard backstops (e.g. concrete wall vs. a dirt berm) are used. For this reason, steel shot is explicitly banned at most indoor shooting ranges. Any shooters who are considering buying ammo loaded with steel for anything other than hunting purposes should first find out if using it won't cause undue hazard to themselves and others.^{[citation needed]}

However, it should be noted that data supporting the danger of firing high velocity shells loaded with steel shot causing barrel wear has not been published and the US equivalent of CIP, SAAMI, does not have any such restrictive limitations on the velocity of commercial steel shotshells sold in the United States. Similarly, shotgun manufacturers selling shotguns in the United States select their own appropriate standards for setting steel hardness for shotgun barrels and for velocities of steel shotshell loaded ammunition.

Some indoor shooting ranges prohibit the use of steel shot over concern of it causing a spark when hitting an object down range and causing a fire.^{[citation needed]}

Shot sizes

Shotshells are loaded with different sizes of shot depending on the target. For skeet shooting, a small shot such as a # 8 or #9 would be used, because range is short and a high density pattern is desirable. Trap shooting requires longer shots, and so a larger shot, up to #7½ would be desired. For hunting game, the range and the penetration needed to assure a clean kill must both be considered. Shot loses its velocity very quickly due to its low sectional density and ballistic coefficient (see external ballistics). Small shot, like that used for skeet and trap, will have lost all appreciable energy by 100 yards or meters, which is why trap and skeet ranges can be located in relatively close proximity to inhabited areas with negligible risk of injury to those outside the range.

Birdshot

12 gauge birdshot shotgun shell.

Birdshot sizes are numbered similar to the shotgun gauges; the smaller the number, the larger the shot. Generally birdshot is just called "shot", such as "number 9 shot" or "BB shot". A useful method for remembering the diameter of numbered birdshot is simply to subtract the shot size from 17. The resulting answer is the diameter of the shot in hundredths of an inch. For example, number 2 shot gives 17-2 = 15, meaning that the diameter of number 2 shot is 15/100 or 0.15". B shot is .170 inches, and sizes go up in .01 increments for BB and BBB or Pellets.

Size	Nominal diameter	Pellets per oz (28 g)		Quantity per lb.[4]
		Lead	Steel
FF	.23" (5.84 mm)		35
F	.22" (5.59 mm)		39
TT	.21" (5.33 mm)
T	.20" (5.08 mm)	36	53
BBB	.190" (4.83 mm)	44	62	550
BB	.180" (4.57 mm)	50	72	650
B	.170" (4.32 mm)
1	.160" (4.06 mm)	72	103	925
2	.150" (3.81 mm)	87	125	1120
3	.140" (3.56 mm)	108	158	1370
4	.130" (3.30 mm)	135	192	1720
5	.120" (3.05 mm)	170	243	2180
6	.110" (2.79 mm)	225	315	2850
7	.100" (2.54 mm)
7½	.095" (2.41 mm)	350		3775
8	.090" (2.29 mm)	410	686	5150
8½	.085" (2.15 mm)	497
9	.080" (2.03 mm)	585	892	7400

Number 11 and number 12 lead shot also exists. Shot of these sizes is used in specialized shotshells designed to be fired at close range (less than four yards) for killing snakes, rats and similar-sized animals. Such shells are typically intended to be fired from handguns, particularly revolvers. See http://firearmsid.com/A_distshotpatt.htm for a photographic comparison of shot sizes that includes examples of these tiny shot. This type of ammunition is produced by Federal and CCI, among others.

Birdshot selection

For hunting, shot size must be chosen not only for the range, but also for the game. The shot must reach the target with enough energy to penetrate to a depth sufficient to kill the game. Lead shot is still the best performer for the money, but environmental restrictions on the use of lead, especially with waterfowl, require steel, bismuth, or tungsten composites. Steel, being significantly less dense than lead, requires larger shot sizes, but is a good choice when cost is a consideration. Steel, however, cannot safely be used in some older shotguns without causing damage to either the bore or to the choke of the shotgun due to the hardness of steel shot. Since tungsten is a very hard metal, it must also be used with care in older guns. Tungsten shot is often alloyed with nickel and iron, softening the base metal. That alloy is approximately 1/3 denser than lead, but far more expensive. Bismuth shot falls in between steel and tungsten shot in both density and cost.

Game	Lead/Tungsten	Steel
Pheasant	4 to 6	2 to 3[5]
Turkey	4 to 6	2 to 3
Quail, dove,	7½ to 8
Rabbit	6 to 7½
Squirrel	6
Geese	BB to 2	TT to 1
Ducks, low	4 to 6	2 to 4
Ducks, high	2 to 4	BB to 2

Buckshot

Larger sizes of shot, large enough that they must be carefully packed into the shell rather than simply dumped or poured in, are called "buckshot" or just "buck". Buckshot is used for hunting larger game, such as deer (hence derivation of the name), and also in riot shotguns and combat shotguns for defensive, police, and military use. Buckshot size is designated by number, with smaller numbers being larger shot; sizes larger than "0" ("aught") are designated by multiple zeros. "00" ("double-aught") is the most commonly used size.

A standard 00 buck shell holds 7-9 pellets. Two types of 00 buckshot are commonly available from suppliers: regular 00 buckshot shells, and reduced-recoil shells favored in law enforcement or home defense use. Low-recoil 00 buckshot allows the shooter to make fast follow-up shots, which may be needed in a combat situation, but are not typically required in hunting (where the main goal is to cleanly take out the game with a single shot). It's also useful as a stepping stone for shooters who are not yet used to the recoil of full-power shells.

Size	Nominal diameter	Pellets/oz
0000 ("quadruple-aught")	.38" (9.7 mm)	5
000 ("triple-aught")	.36" (9.1 mm)	6
00 ("double-aught")	.33" (8.4 mm)	8
0 ("aught")	.32" (8.1 mm)	9
1	.30" (7.6 mm)	10
2	.27" (6.9 mm)	15
3	.25" (6.4 mm)	18
4	.24" (6 mm)	21

Shotshells and patterning

Most modern sporting shotguns have interchangeable choke tubes to allow the shooter to change the spread of shot that comes out of the gun. In some cases, it is not practical to do this; the gun might have fixed choke, or a shooter firing at receding targets may want to fire a wide pattern immediately followed by a narrower pattern out of a single barrelled shotgun. The spread of the shot can also be altered by changing the characteristics of the shell.

Narrower patterns

A buffering material, such as granulated plastic,^[6] sawdust, or similar material can be mixed with the shot to fill the spaces between the individual pellets. When fired, the buffering material compresses and supports the shot, reducing the deformation the shot pellets experience under the extreme acceleration. Copper plated lead shot, steel, bismuth, and tungsten composite shot all have a hardness greater than that of plain lead shot, and will deform less as well. Reducing the deformation will result in tighter patterns, as the spherical pellets tend to fly straighter. One improvised method for achieving the same effect involves pouring molten wax or tar into the mass of shot.^[6] Another is a partial ring cut around the case intended to ensure that the shot comes out tightly bunched along with the portion of the case forward of the cut, creating a 'cut-shell'.^[7] This can be dangerous, as it is thought to cause higher chamber pressures- especially if part of the shell remains behind in the barrel and is not cleared before another shot is fired.^[7][8]

Wider patterns

Shooting the softest possible shot will result in more shot deformation and a wider pattern. This is often the case with cheap ammunition, as the lead used will have minimal alloying elements and be very soft. Spreader wads are wads that have a small plastic or paper insert in the middle of the shot cup, usually a cylinder or "X" cross-section. When the shot exits the barrel, the insert helps to push the shot out from the center, opening up the pattern. Often these result in inconsistent performance, though modern designs are doing much better than the traditional improvised solutions. Intentionally deformed shot (hammered into ellipsoidal shape) or cubical shot will also result in a wider pattern, much wider than spherical shot, with more consistency than spreader wads. Spreader wads and non-spherical shot are disallowed in some competitions. Hunting loads that use either spreaders or non-spherical shot are usually called "brush loads", and are favored for hunting in areas where dense cover keeps shot distances very short.

Spread

A shotgun's shot spread refers to the pattern that the projectiles (or shot) leave behind on a target.^[9] Most shotgun shells contain at least several metal shots, in order to increase the likelihood that a target will be hit. This is especially useful for hunting small game such as birds, rabbits, and other animals that fly or move quickly and can unpredictably change their direction of travel. However, some shotgun shells only contain one metal shot, known as a slug, for hunting large game such as deer.

As the shot leaves the barrel upon firing, the shot is close together. But as the shot moves farther away, the individual pellets increasingly spread out and disperse. Because of this, the effective range of a shotgun, when firing a multitude of shot, is limited to approximately 20 to 50 m (22 to 55 yd). To control this effect, shooters select or use a constriction within the barrel of a shotgun called a choke. The choke, whether selectable or fixed within a barrel, effectively reduces the diameter of the barrel, forcing the shot even closer together as it leaves the barrel, thereby increasing the effective range. The tighter the choke, the more narrow the barrel. Consequentially, the effective range of a shotgun is increased with a tighter choke, as the shot column is held tighter over longer ranges. Hunters or target shooters can install several types of chokes, on guns having selectable chokes, depending on the range at which their intended targets will be located. For fixed choke shotguns, different shotguns are often selected for the intended hunting application at hand. From tightest to loosest, the various chokes are: full choke, improved modified, modified, improved cylinder, skeet, and cylinder bore.^[10]

A hunter who intends to hunt an animal such as rabbit or grouse, knows that the animal will be encountered at a close range (usually within 20 m (22 yd)), and will be moving very quickly. So, an ideal choke would be a cylinder bore (the loosest) as the hunter wants the shot to spread out as quickly as possible. If this hunter was using a full choke (the tightest) at 20 m (22 yd), the shot would be very close together and cause an unnecessarily large amount of damage to the rabbit, or, alternatively, a complete miss of the rabbit. This would waste virtually all of the meat for a hit, as the little amount of meat remaining would be overly-laden with shot and rendered inedible. By using a cylinder bore, this hunter would maximize the likelihood of a kill, and maximize the amount of edible meat. Contrarily, a hunter who intends to hunt geese knows that a goose will likely be approximately 50 m (55 yd) away, so, that hunter would want to delay the spread of the shot as much as possible by using a full choke. By using a full choke for targets that are farther away, the shooter again maximizes the likelihood of a kill, and maximizes the amount of edible meat. As well, this guarantees a swift and humane kill as the target would be hit with enough shot to kill quickly instead of only wounding the animal.

For older shotguns having but one fixed choke, intended primarily for equally-likely use against rabbits, squirrels, quail, doves, and pheasant, an often-chosen choke is the improved cylinder, in a 28 inches (710 mm) barrel, making the shotgun suitable for use as a general all-round hunting shotgun, without having excess weight. Shotguns having fixed chokes intended for geese, in contrast, are often found with full choke barrels, in longer lengths, and are much heavier, being intended for fixed use within a blind. Defensive shotguns with fixed chokes generally have a cylinder bore choke. Likewise, shotguns intended primarily for use with slugs invariably also are found with a choke that is a cylinder bore.

See also

• Breaching round
• Lead shot
• Rat-shot
• Shotgun slug

References

1. ^ http://www.theboxotruth.com/docs/bot43.htm
2. ^ Scottish Association for Country Sports' Shotgun definition
3. ^ http://www.shootingillustrated.com/index.php/8170/snake-loads/
4. ^ Tungsten shot table, used with permission.
5. ^ After bagging 300 birds, researchers declare that No. 2 is best steel shot size for roosters by Craig Bihrle. Reprinted with permission.
6. ^ ^{a b} Krishan Vij. Textbook of Forensic Medicine and Toxicology : Principles and Practice, 5/e. p. 240. http://books.google.com/books?id=pOd2EVL5xAwC&pg=PA240. 
7. ^ ^{a b} George C. Nonte. Firearms encyclopedia. Harper & Row. p. 76. ISBN 9780060132132. "A shotshell which has been cut partially through forward of the head in hope of reducing shot dispersion." 
8. ^ Julian Sommerville Hatcher (1935). Textbook of firearms investigation, identification and evidence: together with the Textbook of pistols and revolvers, Volume 3. Small-arms technical publishing company. p. 61. 
9. ^ "Shotgun Pattern Testing". FirearmsID.com. http://firearmsid.com/A_distshotpatt.htm. Retrieved 2010-05-13. 
10. ^ "Shot spread". Homestudy.ihea.com. http://homestudy.ihea.com/aboutfirearms/13b_spread.htm. Retrieved 2010-05-13. 

External links

• "How They Make Shotgun Shells" , October 1951, Popular Science