Shotgun shell A shotgun shell or shotshell is a self - contained cartridge loaded with lead shot or a shotgun slug which is designed to be fired from a shotgun . Most shotgun shells are designed to be fired from a smoothbore barrel , but dedicated shotguns with rifled barrels may take a number of different rounds . A rifled barrel will increase the accuracy of slugs , but makes it unsuitable for firing shot , as it imparts a spin to the shot cup , causing a centrifugal force that makes the shot form a hollow " O " shape in flight . 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 . Early shotgun shells used brass cases , not very unlike rifle cartridge cases of the same era . These brass shotgun hulls or cases closely resembled rifle cartridges , in terms of both the head and primer portions of the shotgun shell , 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 shell casings . No roll crimp or fold crimp was used on these early brass cases , although roll crimps were eventually used by some manufacturers to hold the overshot wad in place securely . The primers on these early shotgun shells were identical to pistol primers of the same diameter . Starting in about 1877 , paper hulls started to replace brass shotgun shells . Paper hulls remained popular for nearly a century , until the late 1960s . These shotgun shells using paper hulls were nearly always roll crimped , although fold crimping also eventually became popular . The primers on these paper hull shotgun shells also changed from the pistol primers used on the early brass shotgun shells to a primer containing both the priming charge and an anvil , unlike rifle and pistol ammunition , making the shotgun shell 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 in the 1960s , plastic cases started to replace paper hulls for shotgun shells . By the 1980s , plastic cases had largely replaced nearly all paper hulls for shotgun shells . Today , modern shotgun shells typically consist of a plastic case , with the base covered in a thin brass covering . As noted previously , 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 longer than primers used for rifle and pistol ammunition . Modern smokeless powder s 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 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 prevents 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 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 ( 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 zone s , 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 crimp ed , 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 . 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 of a pound . This measurement comes from the time when early cannon s 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 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 . 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 . 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 . 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 . Non shotgun calibres . Shotshells are also available in non - shotgun calibers , for use in rifled barrels from . 22 Long Rifle upwards through . 38 Special to . 44 Magnum ; these are often used in revolver s to kill 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 similar revolver dubbed the " Governor , " which not only shoots . 45 Colt and . 410 shotshells but also . 45 ACP with the aid of moon clips . 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 / cm , and with there being 7 , 000 grains to a pound , the following formula results : This formula accurately estimates the diameter ( d ) 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 , lead - loaded ammunition must be used carefully by hunters in Europe . 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 , and 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 . 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 . Another problem is ricochet . Steel is very elastic and can reflect back to the shooter . 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 . 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 . In metric sizes it is easy to remember that nr . 5 shot is 3 mm . Each number up or down is 0 . 25 mm more or less in diameter . So Nr . 7 shot is 2 . 5 mm . There are small differences in size of Italian , standard ( European ) and English shot to make matters more complex . 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 . 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 lead is not legal and 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 . This is debatable because steel shot is always in a plastic wad . Only in tight choked guns the amount , size and speed of steel shot , combined with penetrating the plastic wall of the wad , can cause damage . The increased pressure in most steel cartridges is a far greater problem , causing more strain to the breech system of the gun . However there are low pressure sporting and hunting versions that can be used safely . 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 . In most European countries ( steel ) shot sizes are limited . For instance in the Netherlands it should be nr . 3 or higher . The general rule of thumb is to go up by two numbers when switching from lead to steel but experience suggests that nr . 4 and 5 are good for hunting most game . However , there are different views on dense patterns versus higher pellet energy . Keeping the distance limitations of steel shot in mind , reducing the maximum distance is advisable . 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 ) . Buckshot size is designated by actual diameter or ( traditionally ) by letter or 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 . The most commonly produced buckshot shell is a 12 gauge , 00 buck shell that holds 9 pellets . Buckshot is generally used for two purposes , self - defense and hunting medium to large game . Loads can be tailored through altering the size of the shot , pellet count , length of the shell , powder charge , and in other ways to fit individual weapons and purposes . For instance , loads of 12 gauge 00 buck are commonly available in 8 to 18 pellets in vendor - stated lengths from 2 . 75 " to 3 . 5 " . On packaging , vendors state the length of the cartridge as expanded after firing . Before firing , the crimped cartridge starts off approximately one half inch shorter . Also , precise length varies depending on manufacturer and model . Reduced - recoil shells are becoming increasingly available . Low - recoil 00 buckshot allows the shooter to make fast follow - up shots , which may be needed in a combat situation . They are also useful for training shooters who are not yet used to the recoil of full - power shells . 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 , 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 . Antimony - lead alloys , 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 . 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 ' . 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 . 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 such as antimony 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 . Most shotgun shells contain multiple pellets in order to increase the likelihood of a target being hit . A shotgun ' s shot spread refers to the two - dimensional pattern that these projectiles ( or shot ) leave behind on a target . Another less important dimension of spread concerns the length of the in - flight shot string from the leading pellet to the trailing one . The use of multiple pellets 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 three - dimensional shot string 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 . To control this effect , shooters may 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 end of the barrel , forcing the shot even closer together as it leaves the barrel , thereby increasing the effective range . The tighter the choke , the narrower the end of 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 or barrels are often selected for the intended hunting application at hand . From tightest to loosest , the various choke sizes are : full choke , improved modified , modified , improved cylinder , skeet , and cylinder bore . 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 - 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 , 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 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 . Also , 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 only 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 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 against distant targets . 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 . Dram equivalence . " Dram " equivalence is sometimes still used as a measure of the powder charge power in a shotgun shell . Today , it is an anachronistic equivalence that represents the equivalent power of a shotgun shell containing this equivalent amount of black - powder measured in drams avoirdupois . A dram in the avoirdupois system is the mass of pound or ounce or 27 . 3 grains . The reasoning behind this archaic equivalence is that when smokeless powder first came out , some method of establishing an equivalence with common shotgun shell loads was needed in order to sell a box of shotgun shells . For example , a shotgun shell containing a 3 or 3 1 / 2 dram load of black - powder was a common hunting field load , and a heavy full power load would have contained about a 4 to 4 - 1 / 2 dram load , whereas a shotgun shell containing only a 2 dram load of black - powder was a common target practice load . A hunter looking for a field or full power load familiar with black - powder shotgun loads would have known exactly what the equivalence of the shotgun shells would have been in the newly introduced smokeless powder . Today , however , this represents a poorly understood equivalence of the powder charge power in a shotgun shell . To further complicate matters , " dram " equivalence was only defined for 12 gauge shotgun shells , and only for lead shot , although it has often been used for describing other gauges of shells , and even steel shot loaded shells . Furthermore , " dram " equivalence only came around about 15 years after smokeless powder had been introduced , long after the need for an equivalence had started to fade , and actual black - powder loaded shotshells had largely vanished . In practice , " dram " equivalence today most commonly equates just to a velocity rating equivalence in fps ( feet - per - second ) , while assuming lead shot . A secondary impact of this equivalence was that common shotgun shells needed to stay the same size , physically , e . g . , 2 - 1 / 2 or 2 - 3 / 4 - inch shells , in order to be used in pre - existing shotguns when smokeless powder started being used to load shotgun shells in the place of black - powder . As smokeless powder did not have to be loaded in the same volume as black - powder to achieve the same power , being more powerful , the volumes of wads had to increase , to fill the shotgun shell enough to permit proper crimps still to be made . Initially , this meant that increased numbers of over powder card wads had to be stacked to achieve the same stack - up length . Eventually , this also lead to the introduction of one - piece plastic wads in the late 1950s through the early 1960s , to add additional wad volumes , in order to maintain the same overall shotgun shell length . Dram equivalence has no bearing on the reloading of shotgun shells with smokeless powder ; loading a shotgun shell with an equivalent dram weight of smokeless powder would cause a shotgun to explode . It only has an equivalence in the reloading of shotgun shells with black - powder .