A chain is a serial assembly of connected pieces, called links made of metal, with an overall character similar to that of a rope in that it is flexible and curved in compression but linear and load-bearing in tension. A chain may consist of two or more links. Chains can be classified by their design, dictated by their use: Those designed for lifting, such as when used with a hoist; those designed for transferring power in machines have links designed to mesh with the teeth of the sprockets of the machine, are flexible in only one dimension. They are known as roller chains, though there are non-roller chains such as block chain. Two distinct chains can be connected using carabiner, or clevis. Uses for chain include: Chain of office, collar or heavy gold chain worn as insignia of office or a mark of fealty in medieval Europe and the United Kingdom Decorating clothing, some people wear wallets with chains connected to their belts, or pants decorated with chains Figaro chain, a decorative style of chain most seen in men's jewellery Omega chain, a pseudo-chain where the'links' are mounted on a backing rather than being interlinked Jewelry chain, many necklaces and bracelets are made out of small chains of gold and silver Bicycle chain, transfers power from the pedals to the drive-wheel of a bicycle, thus propelling it Chain drive, the main feature that differentiated the safety bicycle Chain gun, type of machine gun, driven by an external power source, sometimes connected by a chain, to actuate the mechanism rather than using recoil Chain pumps, type of water pump where an endless chain has positioned on it circular discs Chainsaw, portable mechanical, motorized saw using a cutting chain to saw wood Flat chain, form of chain used chiefly in agricultural machinery Ladder chain, a light wire chain used with sprockets for low torque power transmission O-ring chain, a specialized type of roller chain Roller chain, the type of chain most used for transmission of mechanical power on bicycles, in industrial and agricultural machinery Timing chain, used to transfer rotational position from the crankshaft to the valve and ignition system on an internal combustion engine with a 2:1 speed reduction.
Ball and chain, phrase that can refer to either the actual restraint device, used to slow down prisoners, or a derogatory description of a person's significant other Belly chain, a physical restraint worn by prisoners, consisting of a chain around the prisoner's waist, to which the prisoner's hands are chained or cuffed Bicycle lock, lockable chain Chain boom, large chains used to exclude warships from harbors and rivers Chain link fencing, fencing that utilizes vertical wires that are bent in a zig zag fashion and linked to each other Chain mail, a type of armor consisting of small metal rings linked together in a pattern to form a mesh. Door chain, a type of security chain on a door that makes it possible to open a door from the inside while still making it difficult for someone outside to force their way inside Gang transport chain, a chain used to shackle two or more inmates together for transport or work outside the facility, forming a chain gang Leg iron chains, an alternative to handcuffs Prisoner transport restraints, a combination which consists of a pair of handcuffs attached by a longer chain to a pair of leg irons Security chain, chain with square edges to prevent cutting with bolt-cutters Chain gun on chain-linked handcuffs the cuffs are held together by a short chain Anchor cable, as used by ships and boats, in British nautical usage it is a cable, not a chain Chain steam shipping Chain-linked Lewis, lifting device made from two curved steel legs Curb chain, used on curb bits when riding a horse High-tensile chain, chain with a high tensile strength used for towing or securing loads Jack chain, a toothed chain used to move logs Lead shank, used on horses that are misbehaving Pull switch, an electrical switch operated by a chain Rigid chain actuator, a type of chain that only bends in one direction, allowing it to operate under compression Snow chains, used to improve traction in snow Lavatory chain, the chain attached to the cistern of an old-fashioned W.
C. in which the flushing power is obtained by a gravity feed from above-head height. Although most cisterns no longer work like that, the phrase "pull the chain" is still encountered to mean "flush the toilet". Chain gun, type of machine gun, driven by an external power source, sometimes connected by a chain, to actuate the mechanism rather than using recoil Chain-shot, a type of ammunition for a cannon, used to inflict damage to the rigging of a sail vessel in naval warfare Chain weapon, a medieval weapon made of one or more weights attached to a handle with a chain Chains can be used as a percussion instrument for special effects, such as in Schönberg's Gurre-Lieder and Janáček's From the House of the Dead. Keychain, a small chain that connects a small item to a keyring Chain sinnet, a method of shortening a rope or other cable while in use or for storage Chain stitch, a sewing and embroidery technique The metal link chain has been in use since at least 225 BC; the prevalent modern symbolism is oppression, due to the use for a mechanical restriction of the liberty of a human or animal.
Chains can symbolize interconnectivity or interdependence. Unicode, in versions 6.x, contains the U+1F517 LINK SYMBOL, which may show chain link. It may denote a hy
A sabot is a structural device used in firearm or cannon ammunition to keep a sub-caliber flight projectile, such as a small bullet or arrow-type projectile, in the center of the barrel when fired, if the bullet has a smaller diameter than the bore diameter of the weapon used. The sabot component in projectile design is more than the thin and deformable seal known as a driving band or obturation ring needed to trap propellant gases behind a projectile, keep the projectile centered in the barrel, when the outer shell of the projectile is only smaller in diameter than the caliber of the barrel. Driving bands and obturators are used to seal these full-bore projectiles in the barrel because of manufacturing tolerances. Driving bands and obturator rings are made from material that will deform and seal the barrel as the projectile is forced from the chamber into the barrel. Small caliber jacketed bullets do not employ driving bands or obturators because the jacket material, for example copper or gilding metal, is deformable enough to serve that function, the bullet is made larger than the barrel for that purpose.
Sabots use driving bands and obturators, because the same manufacturing tolerance issues exist when sealing the saboted projectile in the barrel, but the sabot itself is a more substantial structural component of the in-bore projectile configuration. Refer to the two APFSDS pictures on the right to see the substantial material nature of a sabot to fill the bore diameter around the sub-caliber arrow-type flight projectile, compared to the small gap sealed by a driving band or obturator to mitigate what is known classically as windage. More detailed cutaways of the internal structural complexity of advanced APFSDS saboted long rod penetrator projectiles can be found at reference 2; the function of a sabot is to provide a larger bulkhead structure that fills the entire bore area between an intentionally designed sub-caliber flight projectile and the barrel, giving a larger surface area for propellant gasses to act upon than just the base of the smaller flight projectile. Efficient aerodynamic design of a flight projectile does not always accommodate efficient interior ballistic design to achieve high muzzle velocity.
This is true for arrow-type projectiles, which are long and thin for low drag efficiency, but too thin to shoot from a gun barrel of equal diameter to achieve high muzzle velocity. The physics of interior ballistics demonstrates why the use of a sabot is advantageous to achieve higher muzzle velocity with an arrow-type projectile. Propellant gasses generate high pressure, the larger the base area that pressure acts upon the greater the net force on that surface. Force, pressure times area, provides an acceleration to the mass of the projectile. Therefore, for a given pressure and barrel diameter, a lighter projectile can be driven from a barrel to a higher muzzle velocity than a heavier projectile. However, a lighter projectile may not fit in the barrel. To make up this difference in diameter, a properly designed sabot provides less parasitic mass than if the flight projectile were made full-bore, in particular providing dramatic improvement in muzzle velocity for APDS and APFSDS ammunition.
Seminal research on two important sabot configurations for long rod penetrators used in APFSDS ammunition, namely the "saddle-back" and "double-ramp" sabot was performed by the US Army Ballistics Research Laboratory during the development and improvement of modern 105mm and 120mm kinetic energy APFSDS penetrators, permitted by the significant recent advancement in the computerized Finite element method in structural mechanics at that time. Upon muzzle exit, the sabot is discarded, the smaller flight projectile flies to the target with less drag resistance than a full-bore projectile. In this manner high velocity and slender, low drag projectiles can be fired more efficiently; the weight of the sabot represents parasitic mass that must be accelerated to muzzle velocity, but does not contribute to the terminal ballistics of the flight projectile. For this reason, great emphasis is placed on selecting strong yet lightweight structural materials for the sabot, configuring the sabot geometry to efficiently employ these parasitic materials at minimum weight penalty.
The purpose of the sabot is to allow a smaller diameter flight projectile to be launched at greater muzzle velocity than if the flight projectile alone were fired from a gun of equal caliber. Firing a smaller-sized projectile wrapped in a sabot raises the muzzle velocity of the projectile. Made of some lightweight material; the sabot consists of several longitudinal pieces held in place by the cart
A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus Vitis. Grapes can be eaten fresh as table grapes or they can be used for making wine, juice, grape seed extract, raisins and grape seed oil. Grapes are a non-climacteric type of fruit occurring in clusters; the cultivation of the domesticated grape began 6,000–8,000 years ago in the Near East. Yeast, one of the earliest domesticated microorganisms, occurs on the skins of grapes, leading to the discovery of alcoholic drinks such as wine; the earliest archeological evidence for a dominant position of wine-making in human culture dates from 8,000 years ago in Georgia. The oldest known winery was found in Armenia, dating to around 4000 BC. By the 9th century AD the city of Shiraz was known to produce some of the finest wines in the Middle East, thus it has been proposed that Syrah red wine is named after Shiraz, a city in Persia where the grape was used to make Shirazi wine. Ancient Egyptian hieroglyphics record the cultivation of purple grapes, history attests to the ancient Greeks and Romans growing purple grapes for both eating and wine production.
The growing of grapes would spread to other regions in Europe, as well as North Africa, in North America. In North America, native grapes belonging to various species of the genus Vitis proliferate in the wild across the continent, were a part of the diet of many Native Americans, but were considered by early European colonists to be unsuitable for wine. In the 19th century, Ephraim Bull of Concord, cultivated seeds from wild Vitis labrusca vines to create the Concord grape which would become an important agricultural crop in the United States. Grapes are a type of fruit that grow in clusters of 15 to 300, can be crimson, dark blue, green and pink. "White" grapes are green in color, are evolutionarily derived from the purple grape. Mutations in two regulatory genes of white grapes turn off production of anthocyanins, which are responsible for the color of purple grapes. Anthocyanins and other pigment chemicals of the larger family of polyphenols in purple grapes are responsible for the varying shades of purple in red wines.
Grapes are an ellipsoid shape resembling a prolate spheroid. Most grapes come from cultivars of Vitis vinifera, the European grapevine native to the Mediterranean and Central Asia. Minor amounts of fruit and wine come from American and Asian species such as: Vitis amurensis, the most important Asian species Vitis labrusca, the North American table and grape juice grapevines, sometimes used for wine, are native to the Eastern United States and Canada. Vitis mustangensis, found in Mississippi, Louisiana and Oklahoma Vitis riparia, a wild vine of North America, is sometimes used for winemaking and for jam, it is native to the entire Eastern U. S. and north to Quebec. Vitis rotundifolia used for jams and wine, are native to the Southeastern United States from Delaware to the Gulf of Mexico. According to the Food and Agriculture Organization, 75,866 square kilometers of the world are dedicated to grapes. 71% of world grape production is used for wine, 27% as fresh fruit, 2% as dried fruit. A portion of grape production goes to producing grape juice to be reconstituted for fruits canned "with no added sugar" and "100% natural".
The area dedicated to vineyards is increasing by about 2% per year. There are no reliable statistics, it is believed that the most planted variety is Sultana known as Thompson Seedless, with at least 3,600 km2 dedicated to it. The second most common variety is Airén. Other popular varieties include Cabernet Sauvignon, Sauvignon blanc, Cabernet Franc, Grenache, Tempranillo and Chardonnay. Commercially cultivated grapes can be classified as either table or wine grapes, based on their intended method of consumption: eaten raw or used to make wine. While all of them belong to the same species, Vitis vinifera and wine grapes have significant differences, brought about through selective breeding. Table grape cultivars tend to have large, seedless fruit with thin skin. Wine grapes are smaller seeded, have thick skins. Wine grapes tend to be sweet: they are harvested at the time when their juice is 24% sugar by weight. By comparison, commercially produced "100% grape juice", made from table grapes, is around 15% sugar by weight.
Seedless cultivars now make up the overwhelming majority of table grape plantings. Because grapevines are vegetatively propagated by cuttings, the lack of seeds does not present a problem for reproduction, it is an issue for breeders, who must either use a seeded variety as the female parent or rescue embryos early in development using tissue culture techniques. There are several sources of the seedlessness trait, all commercial cultivators get it from one of three sources: Thompson Seedless, Russian Seedless, Black Monukka, all being cultivars of Vitis vinifera. There are more than a dozen varieties of seedless grapes. Several, such as Einset Seedless, Benjamin Gunnels's Prime seedless grapes and Venus, have been cultivated for hardiness and quality in the cold climates of northeastern United States and southern Ontario. An offset to the improved eating quality of seedlessness is the loss of potential health benefits provided by the enriched phytochemical conten
Tin is a chemical element with the symbol Sn and atomic number 50. It is a post-transition metal in group 14 of the periodic table of elements, it is obtained chiefly from the mineral cassiterite, which contains stannic oxide, SnO2. Tin shows a chemical similarity to both of its neighbors in group 14, germanium and lead, has two main oxidation states, +2 and the more stable +4. Tin is the 49th most abundant element and has, with 10 stable isotopes, the largest number of stable isotopes in the periodic table, thanks to its magic number of protons, it has two main allotropes: at room temperature, the stable allotrope is β-tin, a silvery-white, malleable metal, but at low temperatures it transforms into the less dense grey α-tin, which has the diamond cubic structure. Metallic tin does not oxidize in air; the first tin alloy used on a large scale was bronze, made of 1/8 tin and 7/8 copper, from as early as 3000 BC. After 600 BC, pure metallic tin was produced. Pewter, an alloy of 85–90% tin with the remainder consisting of copper and lead, was used for flatware from the Bronze Age until the 20th century.
In modern times, tin is used in many alloys, most notably tin/lead soft solders, which are 60% or more tin, in the manufacture of transparent, electrically conducting films of indium tin oxide in optoelectronic applications. Another large application for tin is corrosion-resistant tin plating of steel; because of the low toxicity of inorganic tin, tin-plated steel is used for food packaging as tin cans. However, some organotin compounds can be as toxic as cyanide. Tin is a soft, malleable and crystalline silvery-white metal; when a bar of tin is bent, a crackling sound known as the "tin cry" can be heard from the twinning of the crystals. Tin melts at low temperatures of about 232 °C, the lowest in group 14; the melting point is further lowered to 177.3 °C for 11 nm particles. Β-tin, stable at and above room temperature, is malleable. In contrast, α-tin, stable below 13.2 °C, is brittle. Α-tin has a diamond cubic crystal structure, similar to silicon or germanium. Α-tin has no metallic properties at all because its atoms form a covalent structure in which electrons cannot move freely.
It is a dull-gray powdery material with no common uses other than a few specialized semiconductor applications. These two allotropes, α-tin and β-tin, are more known as gray tin and white tin, respectively. Two more allotropes, γ and σ, exist at temperatures above 161 pressures above several GPa. In cold conditions, β-tin tends to transform spontaneously into α-tin, a phenomenon known as "tin pest". Although the α-β transformation temperature is nominally 13.2 °C, impurities lower the transition temperature well below 0 °C and, on the addition of antimony or bismuth, the transformation might not occur at all, increasing the durability of the tin. Commercial grades of tin resist transformation because of the inhibiting effect of the small amounts of bismuth, antimony and silver present as impurities. Alloying elements such as copper, bismuth and silver increase its hardness. Tin tends rather to form hard, brittle intermetallic phases, which are undesirable, it does not form wide solid solution ranges in other metals in general, few elements have appreciable solid solubility in tin.
Simple eutectic systems, occur with bismuth, lead and zinc. Tin was one of the first superconductors to be studied. Tin can be attacked by acids and alkalis. Tin can be polished and is used as a protective coat for other metals. A protective oxide layer prevents further oxidation, the same that forms on pewter and other tin alloys. Tin helps to accelerate the chemical reaction. Tin has ten stable isotopes, with atomic masses of 112, 114 through 120, 122 and 124, the greatest number of any element. Of these, the most abundant are 120Sn, 118Sn, 116Sn, while the least abundant is 115Sn; the isotopes with mass numbers have no nuclear spin, while those with odd have a spin of +1/2. Tin, with its three common isotopes 116Sn, 118Sn and 120Sn, is among the easiest elements to detect and analyze by NMR spectroscopy, its chemical shifts are referenced against SnMe4; this large number of stable isotopes is thought to be a direct result of the atomic number 50, a "magic number" in nuclear physics. Tin occurs in 29 unstable isotopes, encompassing all the remaining atomic masses from 99 to 137.
Apart from 126Sn, with a half-life of 230,000 years, all the radioisotopes have a half-life of less than a year. The radioactive 100Sn, discovered in 1994, 132Sn are one of the few nuclides with a "doubly magic" nucleus: despite being unstable, having lopsided proton–neutron ratios, they represent endpoints beyond which stability drops off rapidly. Another 30 metastable isomers have been characterized for isotopes between 111 and 131, the most stable being 121mSn with a half-life of 43.9 years. The relative differences in the abundances of tin's stable isotopes can be explained by their different modes of formation in stellar nucleosynthesis. 116Sn through 120Sn inclusive are formed in the s-process in most stars and hence they are the most common isotopes, while 122Sn and 124Sn are only formed in the r-process (rapid neutr
CSS Georgia (ironclad)
CSS Georgia known as State of Georgia and Ladies' Ram, was an ironclad warship built in Savannah, Georgia in 1862 during the American Civil War. The Ladies' Gunboat Association raised $115,000 for her construction to defend the port city of Savannah. Commanded by Lieutenant Washington Gwathmey, CSN, the new warship was employed to defend the river channels below Savannah, using her cannons to prevent a Union advance on the city from the sea; when her steam engines turned out to lack sufficient power for offensive use, Georgia was anchored in the Savannah River as a floating battery, protecting both the city and Fort Jackson. Georgia had been in service about 20 months, when Sherman's March to the Sea captured Savannah by land on December 21, 1864, her Confederate crew scuttled the ship to use against the South. In 1866 the ship's railroad iron armor was salvaged and the wooden hull was shattered by the underwater charges used to remove it; the wreck was left alone and forgotten. In 1968 Georgia was rediscovered during a dredging operation of the Savannah River.
The wreck was left untouched, although accidental impacts from dredging equipment and the anchors marking the site location may have damaged what remained. By 1992, all, survived were portions of her forward and aft casemates and parts of her engines, including the boilers, shafts and condensers. Several of her cannon were located along with assorted ordnance. In May 2012 the United States Army Corps of Engineers budgeted $14 million to raise the remains of the ironclad to allow for further dredging. Archeologists working for the USACE Savannah District, assisted by teams from the United States Navy, raised a 64 square feet section of Georgia on November 12, 2013. Further relics are being recovered during an ongoing nine-month salvage operation in 2015, as an initiative to upgrade waterway access for deep sea vessels requires its dredging to 47 feet; as of April 2015, USACE, with archaeologists from Texas A&M University, had recovered over 1000 artifacts. The removal of ordnance and the lifting of the major remains of the casemates and machinery occurred in June–August 2015.
In the 1980s a photograph was discovered that shows the Georgia, but it was discovered to be fake. Georgia was placed on the National Register of Historic Places in 1987. Fort James Jackson, CSS Georgia sank in the river next to Fort James Jackson Bisbee, Saxon T.. Engines of Rebellion: Confederate Ironclads and Steam Engineering in the American Civil War. Tuscaloosa, Alabama: University of Alabama Press. ISBN 978-0-81731-986-1. USACE Savannah CSS Georgia project website 2015 Raise the Wreck Festival Media related to CSS Georgia at Wikimedia Commons This article incorporates text from the public domain Dictionary of American Naval Fighting Ships
Ballistics is the field of mechanics that deals with the launching, flight and effects of projectiles bullets, unguided bombs, rockets, or the like. A ballistic body is a body with momentum, free to move, subject to forces, such as the pressure of gases in a gun or a propulsive nozzle, by rifling in a barrel, by gravity, or by air drag. A ballistic missile is a missile only guided during the brief initial powered phase of flight, whose trajectory is subsequently governed by the laws of classical mechanics, in contrast to a cruise missile, aerodynamically guided in powered flight; the earliest known ballistic projectiles were stones and spears, the throwing stick. The oldest evidence of stone-tipped projectiles, which may or may not have been propelled by a bow, dating to c. 64,000 years ago, were found in Sibudu Cave, present day-South Africa. The oldest evidence of the use of bows to shoot arrows dates to about 10,000 years ago, they had shallow grooves on the base. The oldest bow so far recovered is about 8,000 years old.
Archery seems to have arrived in the Americas with the Arctic small tool tradition, about 4,500 years ago. The first devices identified as guns appeared in China around 1000 AD, by the 12th century the technology was spreading through the rest of Asia, into Europe by the 13th century. After millennia of empirical development, the discipline of ballistics was studied and developed by Italian mathematician Niccolò Tartaglia in 1531, although he continued to use segments of straight-line motion, conventions established by Avicenna and Albert of Saxony, but with the innovation that he connected the straight lines by a circular arc. Galileo established the principle of compound motion in 1638, using the principle to derive the parabolic form of the ballistic trajectory. Ballistics was put on a solid scientific and mathematical basis by Isaac Newton, with the publication of Philosophiæ Naturalis Principia Mathematica in 1687; this gave mathematical laws of motion and gravity which for the first time made it possible to predict trajectories.
The word ballistics comes from the Greek βάλλειν ballein, meaning "to throw". A projectile is any object projected into space by the exertion of a force. Although any object in motion through space is a projectile, the term most refers to a ranged weapon. Mathematical equations of motion are used to analyze projectile trajectory. Examples of projectiles include balls, bullets, artillery shells, etc. Throwing is the launching of a projectile by hand. Although some other animals can throw, humans are unusually good throwers due to their high dexterity and good timing capabilities, it is believed that this is an evolved trait. Evidence of human throwing dates back 2 million years; the 90 mph throwing speed found in many athletes far exceeds the speed at which chimpanzees can throw things, about 20 mph. This ability reflects the ability of the human shoulder muscles and tendons to store elasticity until it is needed to propel an object. A sling is a projectile weapon used to throw a blunt projectile such as a stone, clay or lead "sling-bullet".
A sling has a small pouch in the middle of two lengths of cord. The sling stone is placed in the pouch; the middle finger or thumb is placed through a loop on the end of one cord, a tab at the end of the other cord is placed between the thumb and forefinger. The sling is swung in an arc, the tab released at a precise moment; this frees the projectile to fly to the target. A bow is a flexible piece of material. A string joins the two ends and when the string is drawn back, the ends of the stick are flexed; when the string is released, the potential energy of the flexed stick is transformed into the velocity of the arrow. Archery is the sport of shooting arrows from bows. A catapult is a device used to launch a projectile a great distance without the aid of explosive devices — various types of ancient and medieval siege engines; the catapult has been used since ancient times, because it was proven to be one of the most effective mechanisms during warfare. The word "catapult" comes from the Latin "catapulta", which in turn comes from the Greek καταπέλτης, itself from, "downwards" and πάλλω, "to toss, to hurl".
Catapults were invented by the ancient Greeks. A gun is a tubular weapon or other device designed to discharge projectiles or other material; the projectile may be solid, gas, or energy and may be free, as with bullets and artillery shells, or captive as with Taser probes and whaling harpoons. The means of projection varies according to design but is effected by the action of gas pressure, either produced through the rapid combustion of a propellant or compressed and stored by mechanical means, operating on the projectile inside an open-ended tube in the fashion of a piston; the confined gas accelerates the movable projectile down the length of the tube imparting sufficient velocity to sustain the projectile's travel once the action of the gas ceases at the end of the tube or muzzle. Alternatively, acceleration via electromagnetic field generation may be employed in which case the tube may be dispensed with and a guide rail substituted. A rocket is a missile, aircraft or other vehicle that obtains thrust from a rocket engine.
Rocket engine exhaust is formed from propella
A shotgun shell is a self-contained cartridge loaded with multiple metallic "shot", which are small spherical projectiles. The shells consist of a plastic tube mounted on a brass base holding a primer; the shot is contained in a small container inside the shell casing. Shot has traditionally been made of lead, but steel, tungsten or bismuth is used due to restrictions on lead. A shotgun shell can contain a large projectile known as a shotgun slug, they can be made with specialty non-lethal rounds such as beanbag rounds, rubber. Shotguns have an effective range of about 45 meters. An old non-lethal round consisted of a shotgun shell loaded with rock salt, which could inflict painful, but deadly and was popular for scaring away trespassers. Other rounds include: Ferret rounds: rounds designed to penetrate a thin barrier and release a gas payload. Bolo rounds: two large lead balls attached by a wire. Piranha rounds: shells full of sharp tacks. Dragon's breath rounds: shells full of chemicals that burn when fired, can ignite a flammable target at close range.
Most shotgun shells are designed to be fired from a smoothbore barrel, but dedicated shotguns with rifled barrels are limited to lead slugs or sabot slugs as "shot" would be spread too wide by the 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. Early shotgun shells used brass cases, not unlike pistol cartridge cases of the same era; these brass shotgun hulls or cases 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 and cork, as well as paperboard, were all used at various times. Waterglass was 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 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 until the late 1960s; these shotgun shells using paper hulls were nearly always roll crimped, although fold crimping eventually became popular. The primers on these paper hull shotgun shells 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 giving way to plastic over powder wads, with card wads, to all plastic wads. Starting in the 1960s, plastic cases started to replace paper hulls for shotgun shells. Modern shotgun shells consist of a plastic case, with the base covered in a thin brass plated steel covering; as noted paper shells used to be common, 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. 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 provide a significant amount of strength, but the difference in appearance provides shooters with a way to differentiate between high and low powered ammunition. The base of the shotshell is thick to hold the large shotgun primer, 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 little space is taken by powder. After the powder comes the wadding or wad; the primary purpose of a wad is to prevent the shot and powder from mixing, to provide a seal that prevents gas from blowing through the shot rather than propelling it. The wad design may 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, the shot cup, which may be separate pieces or be one part. The powder wad acts as the gas seal, is placed over the powder; the cushion comes next, it is designed to compress under pressure, to act as a shock absorber and minimize the deformation of the shot. Cushions are universally made of plastic with crumple zones, although for game shooting in areas grazed by farm stock or wildlife biodegradable fibre wads are preferred; the shot cup is the last part of the shell, 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 almost universally plastic; the shot fills the shot cup, the shotgun shell is crimped, or rolled closed. Shotgun shells are measured by "gauge", the weight, in fractio