# Smoothbore weapons

Smoothbore weapons are weapons with a smooth surface on the inside of the barrel.

## History and development

Most firearms up until the middle of the 19th century were smoothbore weapons. They used a round shot with a relatively low range. Since the shot's trajectory wasn't stabilized these weapons were rather imprecise compared to modern weapons. The hand cannon of the 13th century was one of these early handguns.
From roughly 1850 onward, guns started to have rifling which guided and directed the projectile in the gun barrel with a sideward spin. This stabilized the trajectory; combined with an adjusted shape it increased the range and the chance of accuracy drastically. Since the 1860s weapons with a rifling in the barrel have been the standard.

## Smoothbore weapons

Smoothbore weapons find a use both in civilian and military areas.

### Hand guns

Early hand guns like pistols, revolvers and rifles were made with smooth bores. Until the 21st century most flare guns had smooth barrels as well.

#### Shotguns

With very few exceptions shotguns have smooth barrels. They used pellet shot and create a "bullet cloud" after leaving the barrel. The resulting loss in accuracy is unimportant; a potential spin of the projectiles would also worsen the bullet cloud since the bullet sheave would spread the shot too much. The spread of the pellets can be varied by using a so-called "choke", which tightens the muzzle of the gun. Shotguns can also be used to shoot shotgun slugs.

### Smoothbore cannon

Weapons with elongated barrels used as tank- and antitank artillery reached their physical limits in the 1960s and designers could no longer improve them. However, the armor of combat vehicles had improved so much that an increase in penetrating power was needed. The power of these kinetic energy penetrators is mainly influenced by kinetic energy and thus mainly the speed of the projectile. The rifling of the barrel as well as the drag created by the driving band and the sides of the barrel slow down the projectile considerably. Projectiles with a greater diameter than the rifling gave rise to a loss of pressure through the gap between barrel and bullet. These conceptual disadvantages could no longer be compensated for, not even by an increase in caliber or propellant charge.
As a result of this the development of smooth bores resurged. The Soviet MT-12 was the first modern weapon/anti-tank gun that utilized a smooth bore and sabot projectiles. With the introduction of the first 115mm smoothbore cannon, the U-5TS first used in the T-62 in the 1950s, began the unstoppable rise of tanks using smooth bores, which continues today.

### Grenade launchers

Grenade launchers have numerous names in different languages. However, all of them describe a steep-firing weapon with indirect fire.
Design-wise the hand-held weapon type "grenade launcher" has to be differentiated from the "grenade pistol" or the "rifle grenade".

#### Stationary grenade launchers

Stationary grenade launchers use a relatively simple construction. They are made of a smooth tube, a ground-plate with the firing pin and the targeting device. In most cases the grenade is inserted into the tube from the top and slowly slides down through gravity. The diameter of the grenade is always smaller than that of the tube; this way, the air that would otherwise build up below it, can escape. Constructions that use a fixed firing pin ignite the propellant at the moment the grenade hits the ground-plate. With higher calibers the firing pin is triggered by pulling a trigger line. The feedback is transferred into the ground through the ground-plate; as a result the grenade launcher can be used as a steep-firing weapon.
The modern grenade launcher is based on the Stokes mortar, a trench mortar, invented in 1915 by Wilfried Stokes. Stokes used the essential construction features, but not the stabilizing grenades at first. The mortar was so small and light that it could be used by infantry in the trenches.
During World War I the first modern grenade launchers were developed and deployed in high numbers. At the end of 1914, stationary warfare became more prevalent and it was hard to get into open combat with the enemy under cover. Steep-firing weapons, however, could still hit the enemy, since they were only slightly or not at all protected from attacks from above. The French first deployed grenade launchers in 1915 at Arras as 'Artillerie de tranchée' (Artillery of the trenches). Both accuracy and range were pretty low though, which led the French to switch to wing-stabilized ammunition.
The German light, medium and heavy mine launcher had stretched pipes, pipe return flow with a lateral angle of 360° and a height adjustment of 50° to 80°. Even though it is called 'mine launcher' it does shoot normal projectiles. The light and medium mine launchers also had the option of 'flat-shooting'; thus they could also be used to attack enemy tanks in a direct line.
Many different grenade launchers were developed between the two World Wars and after World War II. Super-heavy grenade launchers, such as the driverless Soviet 430-mm-grenade launcher 2B1 Oka, which was intended to launch nuclear missiles were among them. The weapons intended to shoot nuclear missiles were replaced by tactical rockets from the 1950s onward. Smaller grenade launchers are still used in great numbers as supporting weapons in the infantry.
* Autonomously driving 430-mm-grenade launcher 2B1 Oka
* 5-cm-light grenade launcher 36
* 82-mm-grenade launcher BM-37
* 120-mm-mortar Thomson-Brandt
* 120-mm-mortar M120

### Grenade launchers as handheld weapons

There is a major difference between handheld grenade launchers and the stationary armament of the same name. The only thing these two have in common is the smooth bore. With these weapons the propellant is stored in a thick-walled cartridge. After ignition the propellant burns away in the cartridge and the gas created flow into the gas outlets in the chamber. This lowers the pressure drastically and as a result the muzzle velocity is decreased, which results in the grenade being propelled at a slower pace. There are two versions of handheld grenade launchers: a fully fledged weapon and an under-mount grenade launcher which can be mounted on an ordnance assault rifle.

### Rocket-propelled grenades

Rocket-propelled grenades (RPGs) are smoothbore weapons that shoot ammunition using wings as stabilizers. During World War II they were used on a large scale for the first time. Nowadays, RPGs are used in various armed forces to combat tanks at close-range.
In modern RPGs propellant charge is ignited in the barrel, which launches the projectile. Propellant gases often escape through an opening in the back in the form of a de Laval nozzle. This led to a reduced recoil. After exiting the weapon, the main propellant is ignited after a few meters, in order not to harm the shooter with the hot propellant gases. These projectiles are wing-stabilized. Shaped charge is mainly used to combat tanks. A spin, therefore, is not desired, as the shaped charge spike would be fanned out due to the Munroe effect and the impact thus reduced.
In the American bazooka, the propellant charge fully burns out when leaving the barrel. This barrel is opened on both ends. Contrary to the design of RPGs, the propellant cartridge is both connected with the projectile and ejected with it. It can hit targets up to a distance of 450m. The bazooka inspired the development of the German Panzerschreck. Smaller RPGs, such as the American M-72 function similarly to the bazooka. The Soviet RPG-18 contains a starting propellant charge and a cruise missile engine. A special feature of this weapon is that the two-part tube is shoved together during transport and pulled apart before shooting. These weapons are designed to be used only once.
The Soviet RPG-7, similar to its predecessor, shoots wing-stabilized grenades. It has a starting propellant charge screwed to the projectile, which ejects the bullet from the barrel. After ten meters of flight, the cruise engine, which accelerates the projectile to 300 m/s, is ignited. The weapon's sighting range is 500m, whereas the actual range is 350m. This weapon design has also been used in various other successors.
In modern RPGs, such as the Panzerfaust 3, plastic bullets are ejected to the rear. As these bullets are denser than gas, a lower exit velocity is needed to compensate the feedback. Since the rear beam is also smaller, these weapons can be shot from buildings. In addition, a smaller propellant charge is needed.
* Panzerfaust and the RPG 54 (below)
* Bazooka
* M72A2
* RPG-18
* Panzerfaust 3

### Rocket launchers

Rocket launchers, given different names in other languages, were originally used to shoot unguided rockets. Since they were used to target whole areas, high precision was not required. The rockets were stabilized in mid-air by means of fixed empennages or ones that fold out after exiting the tube. The main difference between rocket launchers and grenade launchers is that the former continue to burn the propellant charge after it has left the tube. By doing so, rocket launchers were able to shoot a lot more propellant charge than grenade launchers. The rocket launchers also maintained the simple design of the gun carriages. This resulted in an increased range and a more powerful impact by means of a greater caliber. Rocket launchers, in contrast to grenade launchers, had no ground support. The tube, therefore, did not have to absorb the pressure of the propellant charge. It only served to guide rockets during the launch. Similarly, constructions utilizing lattice tubes, lattice frames (called "throwing frames" by the Wehrmacht) or simple starting rails are also possible.
The first operational systems were designed in the Soviet Union and Germany at the beginning of the Second World War. While the first Soviet systems, such as the BM-13, used rails to guide rockets during the launch, smoothbore tubes were used in the Nebelwerfers designed in Germany using former grenade launchers.
In the Multiple Launch Rocket System, which is called MARS in the German military, the rocket is inserted into a smoothbore tube in the launch container. Nowadays rocket launcher systems are suited for precision ammunition. Here the projectiles are guided in the final phase of the flight using aerodynamic control surfaces.

### Smooth bores as starting devices for guided missiles

Overall, smoothbore weapons are used to start various rockets. This ranges from portable air defense and anti-tank missile systems, such as the 9K115-2 Metis-M and the 9K32 Strela-2, to starting devices for long-range air defense missiles. Normally, the launch pipe is designed to be a so-called launch container. This means they can be stored for a long time without undergoing maintenance. Launch containers used for shooting unguided air-ground missiles, such as the UB-32 of the S-5, also have smooth bores.
* 9K51 Grad (BM-21) with a guide groove in the bore
* Launch container MLRS
* 9К115-2 Metis-M
* 9K32 Strela-2
* S-300P Angara
* Launch container UB-32 for S-5 rockets

### Recoilless rifles

Recoilless rifles combine the advantages of both grenade launchers and Panzerfausts. Also, they are constructed similarly to the latter. As grenade launchers are mostly used in direct fire they are thus not suited for combating tanks. A downside of Panzerfausts is that they have a low range. Recoilless rifles are much lighter than conventional rifles of the same caliber, but still can shoot a comparable amount of explosives. Therefore, they are mostly used by mobile forces, such as airborne forces. Nowadays, anti-tank guided missile systems have mostly replaced these weapons, but certain weapons such as the Soviet SPG-9 are still used in some armies. In contrast to rocket launchers, the propellant fully burns in the weapons' barrel. In recoilless rifles, the majority of gunpowder gases flow out of the weapon in opposite direction to the bullet flight direction. By doing so, the barrel had to endure less gas pressure and was easier to be built.
The 7.5 cm Leichtgeschütz 40, 10.5 cm Leichtgeschütz 40 and the 10.5 cm Leichtgeschütz 42 used a cartridge with a synthetic floor made out of bakelite. The propellants' explosion destroyed them. The propellant gases escaped through an opening, shaped like a de Laval nozzle, at the end of the weapon.
In Great Britain, Dennistoun Burney developed a system with holes in the chamber, which is surrounded by a second chamber in a ring. The second chamber ended with gas outlet openings for discharging the propellant gases. The cartridges' casing contains holes that are closed by brass coverings. When the propellant gas is ignited, the strips tear open and expose the gas outlet openings of the cartridge. These gases stream through the holes of the first chamber into the second chamber and from there through the gas outlet openings into the open. To the back, the barrel is closed by a breechblock, which enables the reloading of the weapon. The Soviet recoilless rifles B-10 and B-11 utilize said construction.
The system by Kroger and Musser, which was developed in the USA, resembles the one of Burney. However, in the system of Kroger and Musser the gas outlet openings on the side were missing. Instead, the propellant gases from the second chamber are discharged to the rear against the direction of firing. Examples for this type of construction are the US-American M40 and the Soviet SPG-9. The 73-mm-smoothbore cannon 2A28 of the infantry fighting vehicle BMP-1 utilizes the model of the SPG-9 and shoots the same ammunition.
Even the Davy Crocket, which was developed to shoot nuclear ammunition was a recoilless cannon.
* B-10, where one can see the gas outlet openings in the second chamber
* B-11
* gSPG-9
* M-40
* 2A28 of the BMP-1
* M28 Davy Crocket

## Weblinks

* Description of the types of large-caliber bullets

## Literatur

* Otto Lueger: Lexikon der gesamten Technik und ihrer Hilfswissenschaften, Band 1, Stuttgart/Leipzig 1920, S. 459–462
* Tillmann Reibert: Die Entwicklung des Granatwerfers im Ersten Weltkrieg, Dissertation zur Erlangung des Doktorgrades der Fakultät für Mathematik, Informatik und Naturwissenschaften der Universität Hamburg, Hamburg 2013
* Friedrich Engels (1972), [mlwerke.de "Die Geschichte des gezogenen Gewehrs"], The Volunteer Journal, for Lancashire and Cheshire, Karl Marx/Friedrich Engels – Werke, 15 (4., unveränderte ed.), Berlin: Dietz {{citation}}: Check |url= value (help); Unknown parameter |werkerg= ignored (|contribution= suggested) (help)