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Caseless ammunition (CL), or rather caseless cartridge, is a configuration of weapon-cartridge that eliminates the
cartridge case A cartridge or a round is a type of pre-assembled firearm ammunition packaging a projectile (bullet, shot, or slug), a propellant substance (usually either smokeless powder or black powder) and an ignition device (primer) within a metallic, ...
that typically holds the
primer Primer may refer to: Arts, entertainment, and media Films * ''Primer'' (film), a 2004 feature film written and directed by Shane Carruth * ''Primer'' (video), a documentary about the funk band Living Colour Literature * Primer (textbook), a te ...
,
propellant A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the ...
and
projectile A projectile is an object that is propelled by the application of an external force and then moves freely under the influence of gravity and air resistance. Although any objects in motion through space are projectiles, they are commonly found i ...
together as a unit. Instead, the propellant and primer are fitted to the projectile in another way so that a cartridge case is not needed, for example inside or outside the projectile depending on configuration. Caseless ammunition is an attempt to reduce the weight and cost of ammunition by dispensing with the case, which is typically precision made of
brass Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wi ...
or
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
, as well as to simplify the operation of repeating guns by eliminating the need to extract and eject the empty case after firing. Its acceptance has been hampered by problems with production expenses, heat sensitivity, sealing, and fragility. Its use to date has been mainly limited to prototypes and low-powered guns, with some exceptions.


Internal propellant caseless ammunition


Description

Older caseless ammunition typically uses a configuration where the primer and propellant get integrated into the bottom of the projectile, much like a rocket. When fired, the propellant gas is vented out the back of the projectile to accelerate it to speed. Unlike rocket projectiles, which have similar configurations, the propellant of "internal propellant caseless ammunition" has an instant burn time like a traditional cartridge (under 0.2 seconds), meaning the propellant burns up before the projectile leaves the barrel. Rocket projectiles, in comparison, have propellant burn times of over 0.2 seconds, usually several seconds, meaning rocket propellant traditionally propels the rocket for a certain distance from the launcher. Another difference is means of fire and stabilization. As a cartridge, internal propellant caseless ammunition is only fired from
gun barrel A gun barrel is a crucial part of gun-type 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-pres ...
s, either closed or recoilless, and achieves ballistic stabilization through longitudinal spinning (
conservation of angular momentum In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational analog of linear momentum. It is an important physical quantity because it is a conserved quantity—the total angular momentum of a closed sy ...
), either by the use of driving bands and
rifling 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 ...
or oblique nozzles for the propellant gas. Rockets, in contrast, can be fired from more platforms than gun barrels, for example, rails, and traditionally use fins for stabilization, either fixed or foldable.


History

An early type of internal propellant caseless ammunition was Walter Hunt's Rocket Ball cartridge. It was developed in the 1850s and the guns using it were sold primarily by Volcanic Repeating Arms. Hunt's Rocket Ball cartridges were severely under-powered and never saw wide acceptance for self-protection, hunting, or military use. During
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
, Germany began an intensive program to research and develop a practical internal propellant caseless ammunition cartridge for military use, which was driven by the rising scarcity of metals, especially copper used to make cartridge cases. The Germans had some success, but not sufficient to produce a caseless cartridge system during the war. One quasi-example which almost entered production was the 55 mm Maschinenkanone MK 155. It used partially combustable cartridges similar to the ones used in the popular Rheinmetall Rh-120 tank gun today. Japan, however, successfully developed an aircraft mounted
autocannon An autocannon, automatic cannon or machine cannon is a fully automatic gun that is capable of rapid-firing large-caliber ( or more) armour-piercing, explosive or incendiary shells, as opposed to the smaller-caliber kinetic projectiles (bul ...
using internal propellant caseless ammunition during the war. Named Ho-301, it was a 40 mm autocannon and saw limited action in the defense of the Japanese home islands during the waning months of the war. After WWII the use of internal propellant caseless ammunition largely disappeared from mainstream weapons development, however the type saw a small resurgence when the
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...
introduced their GP-25 40 mm internal propellant caseless under-barrel grenade launcher in 1978. This was followed by the Russian-developed
AGS‑40 Balkan AGS‑40 Balkan is a Russian 40 mm caseless automatic grenade launcher and successor to AGS-17 and AGS-30, introduced and adopted by the Russian military. Design The AGS-40 uses 40 mm CL (caseless) grenades with a range of 2,500 m (compared to ...
40 mm internal propellant caseless automatic grenade launcher in 2017.


Issues

Since propellant is blasted out the back of the projectile during fire, a lot of historical guns using internal propellant caseless ammunition have had problems with residue buildup from the propellant, leading to malfunctions. To decrease residue buildup, historical systems have often been forced to use lower amounts of propellant in the ammunition or adopting a recoilless solution for the gun where some of the burning propellant is vented out the back of the gun when firing. This, however, causes problems on its own as less propellant is being used to propel the ammunition, leading to less potent
muzzle velocities Muzzle velocity is the speed of a projectile (bullet, pellet, slug, ball/shots or shell) with respect to the muzzle at the moment it leaves the end of a gun's barrel (i.e. the muzzle). Firearm muzzle velocities range from approximately to i ...
, often under the
speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as we ...
(~). This is equal to the muzzle-velocities of many mortar-weapons which are meant to be fired at high angles of elevation with heavy projectile arcs. Caseless ammunition weapons are often meant for horizontal fire, meaning that highly sub-sonic ammunition leads to very limited range and poor accuracy due to the rapid loss of projectile velocity.


External propellant caseless ammunition


Description

Modern caseless ammunition typically uses a configuration in which the primer and projectile gets integrated into a solid mass of external propellant (originally
nitrocellulose Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, pyroxylin and flash string, depending on form) is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and ...
), cast to form the body of the cartridge. Cavities exist in the body to accept the bullet and a primer (both of which are glued into place). The completed cartridge might also contain a booster charge of powdered propellant to help ignite the body and provide initial thrust to the bullet. Many of these external propellant caseless cartridges are also telescoped, with the bulk of the bullet held within the body of the cartridge, to cut down on cartridge length. A shorter cartridge cuts down on the distance the firearm's action must reciprocate to load a new round, which allows for higher cyclic rates and greater probability of multiple hits on a target at long range. Lack of a case also reduces the weight of the cartridge substantially, especially in small bore rifles. For example, the external propellant caseless ammunition designed by Austrian inventor Hubert Usel (1926–2010) for the Voere VEC-91 weighs about one third as much as regular ammunition for the same caliber.


Issues

While it seems a simple operation to replace the case with a piece of solid propellant, the cartridge case provides more than just a way to keep the cartridge components together, and these other functions must be replaced if the case is to be replaced. External propellant caseless ammunition is not without its drawbacks, and it is these drawbacks that have kept modern external propellant caseless ammunition from achieving wider success.


Heat sensitivity

The first major problem, of special concern in military applications, which often involve sustained firing, is the heat sensitivity of the ammunition. Nitrocellulose, the primary component of modern
gunpowder Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, carbon (in the form of charcoal) and potassium nitrate (saltpeter). T ...
, ignites at a relatively low temperature of around 170 °C (338 °F). One of the functions of the metallic cartridge case is as a
heat sink A heat sink (also commonly spelled heatsink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, ...
; when extracted after firing, every metallic case carries away a significant amount of the heat from the combustion of the propellant, slowing the rate at which heat builds up in the chamber. The thermal insulation provided by the case also works the other way around, shielding the propellant from built-up heat in the chamber walls. Without a case to provide these functions, external propellant caseless rounds using nitrocellulose will begin to
cook off ''Cook Off'' is a 2017 Zimbabwean romantic comedy film written and directed by Tomas Brickhill. Set in contemporary middle class society of Harare, the film stars Tendaiishe Chitima, Fungai Majaya and Tehn Diamond. Production of the film was ...
, firing from the residual chamber heat, much sooner than cased cartridges do. Cooking off can be avoided by designing the weapon to fire from an open bolt, but this introduces other problems, and thus is only suitable for smaller calibre
machine gun A machine gun is a fully automatic, rifled autoloading firearm designed for sustained direct fire with rifle cartridges. Other automatic firearms such as automatic shotguns and automatic rifles (including assault rifles and battle rifles ...
s and
submachine gun A submachine gun (SMG) is a magazine-fed, automatic carbine designed to fire handgun cartridges. The term "submachine gun" was coined by John T. Thompson, the inventor of the Thompson submachine gun, to describe its design concept as an autom ...
s. The normal solution to the problem of heat is to increase the heat resistance by switching to a propellant with a higher ignition temperature, typically a non-crystalline explosive carefully formulated to provide an appropriate rate of combustion. Heckler & Koch, in concert with Dynamit Nobel, managed such a task by producing relatively heat-resistant external propellant caseless ammunition.


Sealing

Another important function provided by the cartridge is to seal the rear of the chamber. During firing of a cased cartridge, the pressure in the chamber expands the metallic case which obturates to the chamber. This prevents gas exiting from the rear of the chamber, and it has also been experimentally shown to provide a significant amount of support to the bolt. Without the case to provide this seal, the firearm design must account for this and provide a means of sealing the rear of the chamber. This problem was also encountered with the Dreyse needle gun; the French Chassepot solved the leaking-breech problem with the addition of a rubber seal to the bolt. Telescoped external propellant caseless rounds must also deal with the issue of blocking the bore, as the bullet is surrounded by propellant. The booster charge is used to address this issue, providing an initial burst of pressure to force the bullet out of the cartridge body and into the barrel before the body combusts.


Fragility

External propellant caseless rounds are limited by the fact that the cartridge body is primarily a propellant, and structural properties are secondary to the combustion properties. The primary issue is one of extraction. While caseless ammunition eliminates the need to extract a fired case, unfired caseless rounds must be extractable to unload the firearm or to clear a misfire. With metallic cases, this ability is provided by a rim or extractor groove machined into the rear of the case. Even in completely plastic bodied cartridges, such as the Activ brand shotgun shells, a thin metal ring is molded into the rim to provide support for the extractor. A secondary issue is that ammunition in use can be exposed to air, water, lubricants, and solvents. Primer and propellant in external propellant caseless rounds is unprotected, while cartridge cases provide a high degree of protection.


External propellant caseless guns

One of the first caseless firearm and ammunition systems produced was made by
Daisy Daisy, Daisies or DAISY may refer to: Plants * ''Bellis perennis'', the common daisy, lawn daisy or English daisy, a European species Other plants known as daisy * Asteraceae, daisy family ** '' Euryops chrysanthemoides'', African bush daisy ** ' ...
, the
airgun An air gun or airgun is a gun that fires projectiles pneumatically with compressed air or other gases that are mechanically pressurized ''without'' involving any chemical reactions, in contrast to a firearm, which pressurizes gases ''c ...
maker, in 1968. The
Daisy V/L The Daisy V/L was the first production rifle for caseless ammunition. It was released in 1968 by Daisy Outdoor Products. In 1961 Case Hough, the president of Daisy Heddon division of Victor Comptometer, purchased the design of a new firearm system ...
rifle uses a .22 caliber (5.5 mm) low-powered external propellant caseless round with no primer. The rifle was basically a spring-piston air rifle, but when used with the V/L ammunition the energy from the compression of the piston heated the air behind the caseless cartridge enough to ignite the propellant, and this generated the bulk of the energy of firing. The Daisy V/L rifle system was discontinued in 1969 after the ATF ruled that it was not an airgun, but a firearm, which Daisy was not licensed to produce. Some assault rifles have used external propellant caseless ammunition. One of the better-known weapons of this type is the G11 made by Heckler & Koch as a potential replacement for the G3 battle rifle. Although the G11 never entered full production, it went through a number of prototype stages as well as field testing, including testing as part of the American Advanced Combat Rifle program. While it was scheduled to be adopted by the West German military with a plan set out to procure 300,000 G11K2 rifles over a period from 1990 to 2002, the expenses created by the
reunification of Germany German reunification (german: link=no, Deutsche Wiedervereinigung) was the process of re-establishing Germany as a united and fully sovereign state, which took place between 2 May 1989 and 15 March 1991. The day of 3 October 1990 when the Ge ...
and the impossibility of modifying the G11 to use NATO-standard ammunition led to the cancellation of the G11 project and the adoption of a cheaper, more conventional NATO-standardised assault rifle, the 5.56mm G36. The G11's caseless ammunition was later used as the basis for the caseless round development in the US
Lightweight Small Arms Technologies The Lightweight Small Arms Technologies (LSAT) program is funded by the U.S. Joint Service Small Arms Program, with the goal of significantly reducing the weight of small arms and their ammunition. Following a series of military programs to investi ...
program. The first commercial external propellant caseless rifle featuring electronic firing was the Voere VEC-91.


Gallery

File:Rocket-Ball (cropped).JPG, Volcanic .41 Rocket Ball internal propellant caseless ammunition cartridge File:J 21R IP.png, Planned armament for the Saab 21R, consisting of four 95 mm internal propellant caseless ammunition cannons mounted in the wings File:VOG-25 7P17 - MAKS2015part7-50.jpg, VOG-25 7P17 internal propellant caseless ammunition for the 40 mm GP-25 under-barrel grenade launcher File:AGS-40 grenade launcher - Oboronexpo2014part4-46 (cropped).jpg, 7P39 internal propellant caseless ammunition for the 40 mm
AGS‑40 Balkan AGS‑40 Balkan is a Russian 40 mm caseless automatic grenade launcher and successor to AGS-17 and AGS-30, introduced and adopted by the Russian military. Design The AGS-40 uses 40 mm CL (caseless) grenades with a range of 2,500 m (compared to ...
automatic grenade launcher


See also

*
Gyrojet 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 req ...
, defunct modern-era caseless-like ammunition consisting of small rockets rather than powder-fired bullets * Polymer-cased ammunition


References

* Starry, Donn A., General. ''Mounted Combat in Vietnam.''
Department of the Army The United States Department of the Army (DA) is one of the three military departments within the Department of Defense of the U.S. The Department of the Army is the federal government agency within which the United States Army (U.S.) is org ...
, Washington D.C., 1978.


External links


Assault Rifle Ammunition History
{{DEFAULTSORT:Caseless Ammunition Ammunition Caseless firearms Military technology Emerging technologies