Agun barrel is a crucial part ofgun-typeweapons such assmallfirearms,artillery pieces, andair guns. It is the straightshooting tube, usually made of rigid high-strengthmetal, through which a contained rapid expansion of high-pressure gas(es) is used to propel aprojectile out of the front end (muzzle) at a high velocity. The hollow interior of the barrel is called thebore, and thediameter of the bore is called itscalibre, usually measured ininches ormillimetres.
The first firearms were made at a time whenmetallurgy was not advanced enough to cast tubes capable of withstanding the explosive forces of earlycannons, so the pipe (often built from staves of metal) needed to be braced periodically along its length for structural reinforcement, producing an appearance somewhat reminiscent of storagebarrels being stacked together, hence the English name.[1]
Gun barrels are usually made of some type of metal ormetal alloy. However, during the lateTang dynasty, Chinese inventors discoveredgunpowder, and usedbamboo, which has a strong, naturally tubular stalk and is cheaper to obtain and process, as the first barrels in gunpowder projectile weapons such asfire lances.[2] The Chinese were also the first to mastercast-iron cannon barrels, and used the technology to make the earliest infantry firearms — thehand cannons. Early European guns were made ofwrought iron, usually with several strengthening bands of the metal wrapped around circular wrought iron rings and then welded into a hollow cylinder.[3]Bronze andbrass were favoured bygunsmiths, largely because of their ease of casting and their resistance to the corrosive effects of the combustion of gunpowder or salt water when used on naval vessels.[4]
Earlyfirearms weremuzzleloaders, with thegunpowder and then theshot loaded from the front end (muzzle) of the barrel, and were capable of only a lowrate of fire due to the cumbersome loading process. The later-inventedbreech-loading designs provided a higher rate of fire, but early breechloaders lacked an effective way of sealing the escaping gases that leaked from the back end (breech) of the barrel, reducing the availablemuzzle velocity.[5] During the 19th century, effectivebreechblocks were invented that sealed a breechloader against the escape of propellant gases.[6]
Early cannon barrels were very thick for theircaliber. This was because manufacturing defects such as air bubbles trapped in the metal were common at that time, and played key factors in many gun explosions; these defects made the barrel too weak to withstand the pressures of firing, causing it to fail and fragment explosively.[7]
A gun barrel must be able to hold in the expanding gas produced by thepropellants to ensure that optimummuzzle velocity is attained by the projectile as it is being pushed out. If the barrel material cannot cope with the pressure within the bore, the barrel itself might suffercatastrophic failure and explode, which will not only destroy the gun but also present a life-threatening danger to people nearby. Modernsmall arms barrels are made ofcarbon steel orstainless steel materials known and tested to withstand the pressures involved. Artillery pieces are made by various techniques providing reliably sufficient strength.[8][9]
Fluting is the removal of material from a cylindrical surface, usually creating rounded grooves, for the purpose of reducing weight. This is most often done to the exterior surface of a rifle barrel, though it may also be applied to thecylinder of arevolver or thebolt of abolt-action rifle. Most flutings on rifle barrels and revolver cylinders are straight, though helical flutings can be seen on rifle bolts and occasionally also rifle barrels.
While the main purpose of fluting is just to reduce weight and improve portability, when adequately done it can retain thestructural strength andrigidity and increase the overallspecific strength. Fluting will also increase thesurface-to-volume ratio and make the barrel more efficient to cool after firing, though the reduced material mass also means the barrel will heat up easily during firing.
Acomposite barrel is a firearm barrel that has been shaved down to be thinner and an exterior sleeve slipped over and fused to it that improves rigidity, weight and cooling. Most common form of composite barrel are those withcarbon fiber sleeves, but there are proprietary examples such as the Teludyne Tech Straitjacket. They are seldom used outsidesports and competition shooting.
A barrel can be fixed to the receiver usingaction threads or rivets. Depending on construction different gun barrels can be used:
Thechamber is the cavity at the back end of abreech-loading gun's barrel where thecartridge is inserted in position ready to be fired. In most firearms (rifles,shotguns,machine guns andpistols), the chamber is an integral part of the barrel, often made by simplyreaming the rear bore of a barrel blank, with a single chamber within a single barrel.[10] Inrevolvers, the chamber is a component of the gun'scylinder and completely separate from the barrel, with a single cylinder having multiple chambers that are rotated in turns into alignment with the barrel in anticipation of being fired.
Structurally, the chamber consists of thebody,shoulder andneck, the contour of which closely correspond to the casing shape of the cartridge it is designed to hold. The rear opening of the chamber is thebreech of the whole barrel, which is sealed tight from behind by thebolt, making the front direction thepath of least resistance during firing. When the cartridge'sprimer is struck by thefiring pin, thepropellant is ignited anddeflagrates, generating high-pressure gas expansion within the cartridge case. However, the chamber (closed from behind by the bolt) restrains the cartridge case (orshell for shotguns) from moving, allowing thebullet (orshot/slug in shotguns) to separate cleanly from the casing and be propelled forward along the barrel to exit out of the front (muzzle) end as a flyingprojectile.
Chambering a gun is the process of loading a cartridge into the gun's chamber, either manually as insingle loading, or via operating the weapon's ownaction as inpump action,lever action,bolt action orself-loading actions. In the case of anair gun, a pellet (or slug) itself has no casing to be retained and will be entirely inserted into the chamber (often called "seating" or "loading" the pellet, rather than "chambering" it) before a mechanically pressurized gas is released behind the pellet and propels it forward, meaning that an air gun's chamber is functionally equivalent to the freebore portion of a firearm barrel.
In the context of firearms design, manufacturing and modification, the word "chambering" has a different meaning, and refers to fitting a weapon's chamber specifically to fire a particularcaliber or model of cartridge.
Thebore is the hollow internallumen of the barrel, and takes up a vast majority portion of the barrel length. It is the part of the barrel where the projectile (bullet, shot, or slug) is located prior to firing and where it gainsspeed andkinetic energy during the firing process. The projectile's status ofmotion while travelling down the bore is referred to as itsinternal ballistics.
Most modern firearms (exceptmuskets, shotguns, mosttank guns, and someartillery pieces) and air guns (except someBB guns) have helical grooves calledriflings machined into the bore wall. When shooting, a rifled bore imparts spin to the projectile about its longitudinal axis, whichgyroscopically stabilizes the projectile'sflightattitude andtrajectory after its exit from the barrel (i.e. theexternal ballistics). Any gun without riflings in the bore is called asmoothbore gun.
When a firearm cartridge is chambered, its casing occupies the chamber but its bullet actually protrudes beyond the chamber into the posterior end of the bore. Even in a rifled bore, this short rear section is without rifling, and allows the bullet an initial "run-up" to build upmomentum before encountering riflings during shooting. The most posterior part of this unrifled section is called afreebore, and is usually cylindrical. The portion of the unrifled bore immediately front of the freebore, called theleade, starts totaper slightly and guides the bullet towards the area where the riflingless bore transitions into fully rifled bore. Together they form the throat region, where the riflings impactfully "bite" into the moving bullet during shooting. The throat is subjected to the greatest thermomechanicalstress and therefore sufferswear the fastest. Throat erosion is often the main determining factor of a gun's barrel life.
Themuzzle is the front end of a barrel from which the projectile will exit.[11] Precisemachining of the muzzle is crucial to accuracy, because it is the last point of contact between the barrel and the projectile. If inconsistent gaps exist between the muzzle and the projectile, escaping propellant gases may spread unevenly and deflect the projectile from its intended path (seetransitional ballistics). The muzzle can also bethreaded on the outside to allow the attachment of different accessory devices.
Inrifled barrels, the contour of a muzzle is designed to keep the rifling safe from damage by intruding foreign objects, so the front ends of the rifling grooves are commonly protected behind a recessedcrown, which also serves to modulate the even expansion of the propellant gases. The crown itself is often recessed from the outside rim of the muzzle to avoid accidental damage from collision with the surrounding environment.
Insmooth bore barrels firing multiple sub-projectiles (such as shotgun shot), the bore at the muzzle end might have a tapered constriction calledchoke to shape the scatter pattern for better range and accuracy. Chokes are implemented as either interchangeable screw-in chokes for particular applications, or as fixed permanent chokes integral to the barrel.
During firing, a bright flash of light known as amuzzle flash is often seen at the muzzle. This flash is produced by both superheated propellant gases radiating energy during expansion (primary flash), and the incompletely combustedpropellant residues reacting vigorously with the fresh supply of ambient air upon escaping the barrel (secondary flash). The size of the flash depends on factors such as barrel length (shorter barrels have less time for complete combustion, hence more unburnt powder), the type (fast- vs. slow-burning) and amount of propellant (higher total amount means likely more unburnt residues) loaded in the cartridge.Flash suppressors ormuzzle shrouds can be attached to the muzzle of the weapon to either diminish or conceal the flash.[11]
The rapid expansion of propellant gases at the muzzle during firing also produce a powerfulshockwave known as amuzzle blast. The audible component of this blast, also known as amuzzle report, is the loud "bang" sound of gunfire that can easily exceed 140decibels and cause permanenthearing loss to the shooter and bystanders. The non-audible component of the blast is aninfrasonicoverpressure wave that can cause damage to nearby fragile objects. Accessory devices such asmuzzle brakes andmuzzle boosters can be used to redirect muzzle blast in order to counter therecoil-inducedmuzzle rise or to assist thegas operation of the gun, andsuppressors (and even muzzle shrouds) can be used to reduce the blastnoise intensity felt by nearby personnel.
