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A smoothbore weapon is one that has a barrel without rifling. Smoothbores range from handheld firearms to powerful tank guns and large artillery mortars.



A 81mm L16 smoothbore mortar L16 smoothbore.png
A 81mm L16 smoothbore mortar

Early firearms had smoothly bored barrels that fired projectiles without significant spin. [1] To minimize inaccuracy-inducing tumbling during flight, their projectiles required an aerodynamically uniform shape, such as a sphere. However, surface imperfections on the projectile and/or the barrel will cause even a sphere to rotate randomly during flight, and the Magnus effect will curve it off the intended trajectory when spinning on any axis not parallel to the direction of travel. [2]

Rifling the bore surface with spiral grooves or polygonal valleys imparts a stabilizing gyroscopic spin to a projectile that prevents tumbling in flight. Not only does this more than counter Magnus-induced drift, but it allows a longer, more streamlined round with greater sectional density to be fired from the same caliber barrel, improving the accuracy, effective range and hitting power.

In the eighteenth century, the standard infantry arm was the smoothbore musket; although rifled muskets were introduced in the early 18th century and had more power and range, they did not become the norm until the middle of the 19th century, when the Minié ball increased their rate of fire to match that of smoothbores. [3]

Artillery weapons were smoothbore until the middle 19th century, and smoothbores continued in limited use until the 1890s. Early rifled artillery pieces were patented by Joseph Whitworth and William Armstrong in the United Kingdom in 1855. In the United States, rifled small arms and artillery were gradually adopted during the American Civil War. However, heavy coast defense Rodman smoothbores persisted in the US until circa 1900 due to the tendency of the Civil War's heavy Parrott rifles to burst and lack of funding for replacement weapons.

Current use

Replica of "Twin Sisters" smoothbores used in the Battle of San Jacinto (1836) Twin Sisters, San Jacinto.jpg
Replica of "Twin Sisters" smoothbores used in the Battle of San Jacinto (1836)

Some smoothbore firearms are still used.

Small arms

A smooth-bore, cast-iron ship's cannon, from the Grand Turk, a replica of a mid-18th century three-masted frigate Grand Turk(28).jpg
A smooth-bore, cast-iron ship's cannon, from the Grand Turk , a replica of a mid-18th century three-masted frigate

A shotgun fires multiple, round shot; firing out of a rifled barrel would impart centrifugal forces that result a doughnut-shaped pattern of shot (with a high projectile density on the periphery, and a low projectile density in the interior). While this may be acceptable at close ranges (some spreader chokes are rifled to produce wide patterns at close range) this is not desirable at longer ranges, where a tight, consistent pattern is required to improve accuracy. [4]

Another smoothbore weapon in use today is the 37-mm riot gun, which fires non-lethal munitions like rubber bullets and teargas at short range at crowds, where a high degree of accuracy is not required. [5]

The Steyr IWS 2000 anti-tank rifle is smoothbore. This can help accelerate projectiles and increase ballistic effectiveness. The projectile is a 15.2 mm fin-stabilized discarding-sabot type with armor-piercing capability which the IWS 2000 was specifically designed to fire. It contains a dart-shaped penetrator of either tungsten carbide or depleted uranium, capable of piercing 40 mm of rolled homogeneous armor at a range of 1,000 m, and causing secondary fragmentation.


USS Monitor (1862) with the muzzle of one of its two 11-inch smoothbore Dahlgren guns showing
USS Monitor (1862) with the muzzle of one of its two 11-inch smoothbore Dahlgren guns showing

The cannon made the transition from smoothbore firing cannonballs to rifled firing shells in the 19th century. However, to reliably penetrate the thick armor of modern armored vehicles many modern tank guns have moved back to smoothbore. These fire a very long, thin kinetic-energy projectile, too long in relation to its diameter to develop the necessary spin rate through rifling. Instead, kinetic energy rounds are produced as fin-stabilized darts. Not only does this reduce the time and expense of producing rifled barrels, it also reduces the need for replacement due to barrel wear.

The first tank with a smoothbore gun was the Soviet T-62, introduced into service in 1961. Today all main battle tanks field them except the British Challenger 2 and Indian Arjun MBT. While the 73 mm gun of the early Soviet infantry fighting vehicles BMP-1 and BMD-1 was a smoothbore, their more recent successors BMP-3 and BMD-4 use a rifled 100 mm gun. The Russian navy conducted experiments with large-caliber smoothbore naval guns, which were halted by budget cuts.

The armour-piercing gun evolution has also shown up in small arms, particularly the now abandoned U.S. Advanced Combat Rifle (ACR) program. The ACR "rifles" used smoothbore barrels to fire single or multiple flechettes (tiny darts), rather than bullets, per pull of the trigger, to provide long range, flat trajectory, and armor-piercing abilities. Just like kinetic-energy tank rounds, flechettes are too long and thin to be stabilized by rifling and perform best from a smoothbore barrel. The ACR program was abandoned due to reliability problems and poor terminal ballistics.

Mortar barrels are typically muzzle-loading smoothbores. Since mortars fire bombs that are dropped down the barrel and must not be a tight fit, a smooth barrel is essential. The bombs are fin-stabilized.

See also

Related Research Articles

A rifle is a long-barrelled firearm designed for accurate shooting, with a barrel that has a helical pattern of grooves (rifling) cut into the bore wall. In keeping with their focus on accuracy, rifles are typically designed to be held with both hands and braced firmly against the shooter's shoulder via a buttstock for stability during shooting. Rifles are used extensively in warfare, self defense, law enforcement, hunting, and shooting sports.

Kinetic energy penetrator

A kinetic energy penetrator is a type of ammunition designed to penetrate vehicle armour using a flechette-like, high-sectional density projectile. Like a bullet, this type of ammunition does not contain explosive payloads and uses purely kinetic energy to penetrate the target. Modern KEP munitions are typically of the armour-piercing fin-stabilized discarding sabot (APFSDS) type.

Bullet Projectile propelled by a firearm, sling, or air gun

A bullet is a kinetic projectile, a component of firearm ammunition that is shot from a gun barrel. The term is from Middle French, originating as the diminutive of the word boulle (boullet), which means "small ball". Bullets are made of a variety of materials, such as copper, lead, steel, polymer, rubber and even wax. Bullets are made in various shapes and constructions, including specialized functions such as hunting, target shooting, training and combat. Modern bullets are often tapered, making them aerodynamic and increasing penetration upon impact. Bullet sizes are expressed by their weights and diameters in both imperial and metric measurement systems. For example: 55 grain .223 caliber bullets are of the same weight and caliber as 3.56 gram 5.56mm caliber bullets. Bullets do not normally contain explosives, but strike or damage the intended target by transferring kinetic energy upon impact and penetration.

Armor-piercing ammunition

Armor-piercing ammunition is a type of projectile designed to penetrate either body armor or vehicle armor.

A muzzleloader is any firearm into which the projectile and usually the propellant charge is loaded from the muzzle of the gun. This is distinct from the modern designs of breech-loading firearms. The term "muzzleloader" applies to both rifled and smoothbore type muzzleloaders, and may also refer to the marksman who specializes in the shooting of such firearms. The firing methods, paraphernalia and mechanism further divide both categories as do caliber.

Rifling Gunsmithing technique

In firearms, rifling is machining helical grooves into the internal (bore) surface of a gun's barrel for the purpose of exerting torque and thus imparting a spin to a projectile around its longitudinal axis during shooting to stabilize the projectile longitudinally by conservation of angular momentum, improving its aerodynamic stability and accuracy over smoothbore designs.


A flechettefleh-SHET is a pointed steel projectile with a vaned tail for stable flight. The name comes from French fléchette, "little arrow" or "dart", and sometimes retains the acute accent in English: fléchette. They have been used as ballistic weapons since World War I. Delivery systems and methods of launching flechettes vary, from a single shot, to thousands in a single explosive round. The use of flechettes as antipersonnel weapons has been controversial.

High-explosive anti-tank Type of shaped charge explosive

High-explosive anti-tank (HEAT) is a type of shaped charge explosive that uses the Munroe effect to penetrate heavy armor. The warhead functions by having an explosive charge collapse a metal liner inside the warhead into a high-velocity superplastic jet; this superplastic jet is capable of penetrating armor steel to a depth of seven or more times the diameter of the charge. The jet's effect is purely kinetic in nature; the round has no explosive or incendiary effect on the target.

Mortar (weapon) Artillery weapon that launches explosive projectiles at high angles

A mortar is usually a simple, lightweight, man-portable, muzzle-loaded weapon, consisting of a smooth-bore metal tube fixed to a base plate with a lightweight bipod mount and a sight. They launch explosive shells in high-arcing ballistic trajectories. Mortars are typically used as indirect fire weapons for close fire support with a variety of ammunition.

Sabot (firearms)

A sabot is a supportive device used in firearm/artillery ammunitions to fit/patch around a projectile, such as a bullet/slug or a flechette-like projectile, and keep it aligned in the center of the barrel when fired. It allows a narrower projectile with high sectional density to be fired through a barrel of much larger bore diameter with maximal accelerative transfer of kinetic energy. After leaving the muzzle, the sabot typically separates from the projectile in flight, diverting only a very small portion of the overall kinetic energy.

Gun barrel Firearm component which guides the projectile during acceleration

A gun barrel is a crucial part of gun-type ranged weapons such as small firearms, artillery pieces and air guns. It is the straight shooting tube, usually made of rigid high-strength metal, through which a contained rapid expansion of high-pressure gas(es) is used to propel a projectile out of the front end (muzzle) at a high velocity. The hollow interior of the barrel is called the bore, and the diameter of the bore is called its caliber, usually measured in inches or millimetres.

Steyr IWS 2000 Anti-materiel rifle

The Steyr IWS 2000 is an Austrian single-shot bolt-action anti-materiel rifle produced by Steyr Mannlicher. IWS stands for Infantry Weapon System. Like many of today's anti-tank rifles, and indeed also tank guns, it is actually a smoothbore weapon and not a true rifle. This can help accelerate projectiles and increase ballistic effectiveness, but the lack of rifling imparting inertial stability requires the projectile to have stabilizing fins. It fires a 15.2×169 mm armor-piercing fin-stabilized discarding-sabot round, and is the first man-portable rifle to use this type of ammunition.

Minié ball A type of conical projectile for mid 19th century rifles.

The Minié ball or Minie ball, is a type of hollow-based bullet designed by Claude-Étienne Minié, inventor of the French Minié rifle, for muzzleloaded rifled muskets. It came to prominence in the Crimean War and the American Civil War. Both the American Springfield Model 1861 and the British Pattern 1853 Enfield rifled muskets, the most common weapons used during the American Civil War, used the Minié ball.

Gyrojet Firearm that fires small rocket projectiles

The Gyrojet is a family of unique firearms developed in the 1960s named for the method of gyroscopically stabilizing its projectiles. Rather than inert bullets, Gyrojets fire small rockets called Microjets which have little recoil and do not require a heavy barrel or chamber to resist the pressure of the combustion gases. Velocity on leaving the tube was very low, but increased to around 1,250 feet per second (380 m/s) at 30 feet (9.1 m). The result is a very lightweight & transportable weapon.

Tank gun

A tank gun is the main armament of a tank. Modern tank guns are large-caliber high-velocity guns, capable of firing kinetic energy penetrators, high explosive anti-tank rounds, and in some cases guided missiles. Anti-aircraft guns can also be mounted to tanks.

Shotgun slug Type of ammunition used mainly in hunting game

A modern shotgun slug is a heavy projectile made of lead, copper, or other material and fired from a shotgun. Slugs are designed for hunting large game, self-defense, and other uses. The first effective modern shotgun slug was introduced by Wilhelm Brenneke in 1898, and his design remains in use today. Most shotgun slugs are designed to be fired through a cylinder bore or an improved cylinder choke, rifled choke tubes, or fully rifled bores. Slugs differ from round-ball lead projectiles in that they are stabilized in some manner.

Steyr ACR Type of Bullpup assault rifle/Flechette rifle

The Steyr ACR was a prototype flechette-firing assault rifle built for the US Army's Advanced Combat Rifle program of 1989/90. Although the Steyr design proved effective, as did most of the weapons submitted, the entire ACR program ended with none of the entrants achieving performance 100% better than the M16A2, the baseline for a successful ACR weapon.

A rifled musket, rifle musket, or rifle-musket is a type of firearm made in the mid-19th century. Originally the term referred only to muskets that had been produced as a smoothbore weapon and later had their barrels replaced with rifled barrels. The term later included rifles that directly replaced, and were of the same design overall as, a particular model of smoothbore musket.

A muzzle-loading rifle is a muzzle-loaded small arm or artillery piece that has a rifled barrel rather than a smoothbore. The term "rifled muzzle loader" typically is used to describe a type of artillery piece, although it is technically accurate for small arms as well. A shoulder arm is typically just called a "rifle", as almost all small arms were rifled by the time breechloading became prevalent. Muzzle and breechloading artillery served together for several decades, making a clear distinction more important. In the case of artillery, the abbreviation "RML" is often prefixed to the guns designation; a Rifled breech loader would be "RBL", or often just "BL", since smoothbore breechloading artillery is almost nonexistent. A muzzle loading weapon is loaded through the muzzle, or front of the barrel. This is the opposite of a breech-loading weapon or rifled breechloader (RBL), which is loaded from the breech-end of the barrel. The rifling grooves cut on the inside of the barrel cause the projectile to spin rapidly in flight, giving it greater stability and hence range and accuracy than smoothbore guns. Hand held rifles were well-developed by the 1740s. A popularly recognizable form of the "muzzleloader" is the Kentucky Rifle, which was actually developed in Pennsylvania. The American Longrifle evolved from the German "Jäger" rifle.

Armour-piercing fin-stabilized discarding sabot

Armour-piercing fin-stabilized discarding sabot (APFSDS), long dart penetrator, or simply dart ammunition, is a type of kinetic energy penetrator ammunition used to attack modern vehicle armour. As an armament for main battle tanks, it succeeds Armour-Piercing Discarding Sabot (APDS) ammunition, which is still used in small or medium caliber weapon systems.


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