Caseless ammunition

Description Older caseless ammunition typically uses a rocket-like configuration which integrates the primer and propellant into the bottom of the projectile and accelerates it by venting propellant gas out the back. 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, preferably inside the chamber. 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. During World War II, 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, which used partially combustible cartridges, similar to the ones used in the popular Rheinmetall Rh-120 tank gun today. Japan, however, successfully developed an aircraft mounted autocannon 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. Issues Since propellant is blasted out the back of the projectile during fire, many 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, often under the speed of sound (~). 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. Gallery File:Rocket-Ball (cropped).JPG|Volcanic .41 Rocket Ball internal-propellant caseless ammunition cartridge File:J 21R IP.png|Proposed CL-armament for the Saab 21R, consisting of four 95 mm internal-propellant caseless cannons mounted in the wings File:Gerasimenko 2ctgs and primer 1.jpeg|7.62 mm Gerasimenko internal-propellant caseless ammunition for the machine pistol File:VOG-25 7P17 - MAKS2015part7-50 (cropped).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 2).jpg|7P39 internal-propellant caseless ammunition for the 40 mm AGS‑40 Balkan automatic grenade launcher == External-propellant caseless ammunition ==

Description Heckler & Koch'', external-propellant caseless ammunition disassembled. The components are, from left to right: the solid propellant, the primer, the bullet, and a plastic cap that serves to keep the bullet centered in the propellant block. Modern caseless ammunition typically uses a configuration in which the primer and projectile gets integrated into a solid mass of external propellant (originally nitrocellulose), 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. 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 firearm propellant, 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; 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, 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 guns and submachine guns. 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. 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. 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 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 program. The first commercial external-propellant caseless rifle featuring electronic firing was the Voere VEC-91. == See also ==