Smoothbore

Asmoothboreweapon is one that has abarrelwithoutrifling.Smoothbores range from handheldfirearmsto powerfultank gunsand large artillerymortars.

History[edit]

Early firearms had smoothly bored barrels that firedprojectileswithout significant spin.^[1]To minimize inaccuracy-inducing tumbling during flight, their projectiles required an aerodynamically uniform shape, such as asphere.However, surface imperfections on the projectile and/or the barrel will cause even a sphere to rotate randomly during flight, and theMagnus effectwill curve it off the intended trajectory when spinning on any axis not parallel to the direction of travel.^[2]

Riflingthe bore surface with spiral grooves orpolygonal valleysimparts a stabilizinggyroscopicspin 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 greatersectional densityto be fired from the samecaliberbarrel, improving theaccuracy,effective rangeandhitting power.

In the eighteenth century, the standard infantry arm was the smoothboremusket;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 theMinié ballincreased their rate of fire to match that of smoothbores.^[3]

Artilleryweapons were smoothbore until the mid-19th century, and smoothbores continued in limited use until the late 19th century. Early rifled artillery pieces were patented byJoseph WhitworthandWilliam Armstrongin the United Kingdom in 1855. In the United States, rifled small arms and artillery were gradually adopted during theAmerican Civil War.However, heavy coast defenseRodman smoothborespersisted in the US until 1900 due to the tendency of the Civil War's heavyParrott riflesto burst and lack of funding for replacement weapons.

Current use[edit]

Some smoothbore firearms are still used.

Small arms[edit]

Ashotgunfires multiple, roundshot;firing out of a rifled barrel would impartcentrifugal forcesthat result a doughnut-shaped pattern of shot (with a high projectiledensityon the periphery, and a low projectile density in the interior). While this may be acceptable at close ranges (some spreaderchokesare 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]

English or French smoothbore flintlock shotgun with an engraved iron mounting

An 1836 Lane & Reed flintlock smoothbore musket.

Another smoothbore weapon in use today is the 37-mmriot gun,which firesless-lethalmunitions likerubber bulletsandteargasat short range at crowds, where a high degree of accuracy is not required.^[5]

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

Artillery and tanks[edit]

The cannon made the transition from smoothbore firingcannonballsto rifled firingshellsin the mid-19th century. However, to reliably penetrate the thick armor of modern armored vehicles many moderntank gunshave moved back to smoothbore. These fire a very long, thinkinetic-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-stabilizeddarts.Not only does this reduce the time and expense of producing rifled barrels, it also reduces the need for replacement due to barrel wear.^{[citation needed]}

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 multipleflechettes(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 poorterminal ballistics.^{[citation needed]}

Mortarbarrels are typicallymuzzle-loadingsmoothbores. 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.

Gallery[edit]

A smooth-bore, cast-iron ship's cannon, from theGrand Turk,a replica of a mid-18th century three-masted frigate	Replica of "Twin Sisters"smoothbores used in theBattle of San Jacinto(1836)	USSMonitor(1862) with the muzzle of one of its two 11-inch smoothboreDahlgren gunsshowing

References[edit]

^Fadala, Sam (17 November 2006).The Complete Blackpowder Handbook.Iola, Wisconsin: Gun Digest Books. p. 308.ISBN 0-89689-390-1.
^Forge, John (24 December 2012).Designed to Kill: The Case Against Weapons Research: The Case Against Weapons Research.Springer. pp. 63–64.ISBN 978-94-007-5736-3.
^Denny, Mark (1 May 2011).Their Arrows Will Darken the Sun: The Evolution and Science of Ballistics.JHU Press. p. 53.ISBN 978-0-8018-9981-2.
^Haag, Michael G.; Haag, Lucien C. (29 June 2011).Shooting Incident Reconstruction.Academic Press. p. 281.ISBN 978-0-12-382242-0.
^Kolman, John A. (1 January 2006).Patrol Response to Contemporary Problems: Enhancing Performance of First Responders Through Knowledge and Experience.Charles C Thomas. p. 102.ISBN 978-0-398-07656-6.

[Fadala2006-1] Fadala, Sam (17 November 2006).The Complete Blackpowder Handbook.Iola, Wisconsin: Gun Digest Books. p. 308.ISBN 0-89689-390-1.

[Forge2012-2] Forge, John (24 December 2012).Designed to Kill: The Case Against Weapons Research: The Case Against Weapons Research.Springer. pp. 63–64.ISBN 978-94-007-5736-3.

[Denny2011-3] Denny, Mark (1 May 2011).Their Arrows Will Darken the Sun: The Evolution and Science of Ballistics.JHU Press. p. 53.ISBN 978-0-8018-9981-2.

[HaagHaag2011-4] Haag, Michael G.; Haag, Lucien C. (29 June 2011).Shooting Incident Reconstruction.Academic Press. p. 281.ISBN 978-0-12-382242-0.

[Kolman2006-5] Kolman, John A. (1 January 2006).Patrol Response to Contemporary Problems: Enhancing Performance of First Responders Through Knowledge and Experience.Charles C Thomas. p. 102.ISBN 978-0-398-07656-6.

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