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25mm Caseless Grenade



The 25mm grenades are based on the same grenades used in the XM25 OICW program, but are caseless and utilize a compressed propellant based on the metal storm and LSAT programs in order to make them smaller and lighter weight, at just 148 grams for a completed cartridge. The grenades are designed to explode mid-air and come with a wide variety of specialty cartridges, ranging from door-breaching rounds, to rubber bullets and smaller FRAG-12 grenades, using a broad assortment of 12 guage cartridges, but can be designed to explode on contact as well. The air-bursting grenades are particularly useful for clearing entrenched enemies from an area, such as inside of bunkers, buildings or behind barriers, as they can detonate in a more opportune location, providing the effect of indirect fire weapons such as mortar or artillery from a much smaller package. Three main variants of the cartridge exist, heavier 25mm grenades, medium 25mm grenades, and lighter 12 gauge specialty cartridges, each designed with a different power level, however primarily the medium and 12 gauge rounds are used. The rounds with an adapter can fire the pike missile, a 1.7 pound guided missile designed to be fired from a 40mm grenade launcher.

Being caseless, the cartridges are smaller than the original counterpart, being just 140 grams per grenade in addition to 8 grams for the propellant and other elements, making them approximately 1/3rd of a pound per grenade. Each cartridge is smaller and lighter than the original grenades, being just 2.75 inches long vs. the 3.8 inches long for the original grenade. The air-bursting mechanism is laser designated, and based on the rotation of the cartridge, which utilizing metal bands to detect the rotation of the rounds in relation to the magnetic field of the earth, detonates after a predesignated distance. Due to the nature of the mechanism the maximum effective range is limited to approximately 700 meters, however the rounds can reach out further without the laser designated mechanism.

Metal Storm Limited was a research and development company based in Brisbane, Australia that specialized in electronically initiated superposed load weapons technology and owned the proprietary rights to the electronic ballistics technology invented by J. Mike O'Dwyer; Metal Storm represented both the name of the company and the technology. The rounds were essentially stacked on top of each other, and fire dsimilarly to a roman candle, which simplified the operating system, and allows for an overall incredibly short size and low weight. While based off of the the 3GL, the grenade launcher is instead designed to fire 25mm grenades, which overall makes the design much smaller (the barrel is roughly 40% smaller in terms of diameter, or about 1.6 times smaller in terms of area), and thus lighter weight. It also utilizes much higher strength polymers based on the XL-200, which decreases the weight of the overall system.

Unlike ordinary cartridges, it instead depends on electricity to ignite the cartridges, which in turn makes the cartridges less susceptible to cook offs (cook offs being rounds firing unintentionally due to heat, which is more common without a brass casing, which acts as a discardable heat sink), being ignited by an electronic primer. Like with the 3GL, 10's of thousands of rounds are capable of being ignited and cycled with the battery life of the weapon, and the system is water proof. Combining improved caseless powders from the G11 and LSAT series of firearms, the newer binder is significantly less sensitive to cook offs than traditional ammunition; while technically fully automatic, with an RPM of 210, the weapon is intended for semiautomatic use, only.

The original caseless ammunition from the G11 had a significant number of problems; the high rate of fire of the weapon itself and lack of cartridge cases made cooking-off a significant problem since the heat buildup in the G11 chamber was immense, due to the chamber having no provision for cooling, as with a reciprocating bolt system which allows hot air to leave the chamber when the bolt is retracted and the chamber is exposed to air. The vertically swivelling chamber furthermore made gas sealing at each end at such high pressures impractical, as opposed to a cross-sectional round-inside-round bolt-to-chamber fit with appropriate gas sealing . To solve this, Heckler and Koch formed a partnership with Dynamit Nobel who redesigned the cartridge to use a new High Ignition Temperature Propellant (HITP). The cook-off problem was reduced, by using a denatured HMX propellant with a special binder and coating for the ammunition that increased the spontaneous ignition temperature by another 100 °C above that of standard, nitrocellulose (180 °C) propellant.

The LSAT program designed by the U.S. based on this technology created new caseless rounds, including the 5.56mm, 7.62mm NATO, and 6.5mm equivalents, instead being just the weight of the powder and projectile. Like the Russian 40mm caseless grenades, the 25mm caseless grenades are lighter weight and smaller, allowing for more rounds to be carried.



12 Gauge Specialty Cartridges
Based on the 12 gauge specialty cartridges similar to those used in the 40mm grenade launcher, they are substantially lighter weight than these cartridges, because they do not require a case to be used. Based heavily on these cartridges, a number of light-weight rounds can be used, including a 14 gram door-breaching cartridge, 14 gram rubber-round, and 32 gram high-explosive grenade. The rounds are extremely lightweight in comparison to these specialty cartridges, due to the lack of a need of a case, and thus are even lighter than polymer cased 12 gauge shotgun rounds. This allows a large number of rounds to be carried, which is particularly useful for room clearing. Approximately 30 door-breaching rounds can be carried for just about a pound, while 12 Frag-12 high explosive grenades can be carried for about a pound. While smaller and weaker than the 140 gram 25mm grenades normally used, the Frag-12 grenades offer a lighterweight, shorter causality range alternative to the 25mm grenade. In situations where less power is desired, they can be used instead. The weapon can typically fire any round that is normally available for a 12 gauge shotgun, however three main variants of the rounds are used.

Door-breaching rounds
The door-breaching rounds use the same material used in the 12 gauge shotgun. Made out of a polymer-clay construction, they are designed to be deliberately weaker than an ordinary shotgun round, as well as lighter weight, using a less dense material than lead, which not only transfers the energy to the target better, but prevents collateral damage as the clay plug disintegrates on contact and does penetrate the skin very deeply, thus being less lethal. As a result of it's lower density, it is a mere 10 grams for the plug, vs. 28+ grams for 12 gauge lead shot, and an additional 14 grams for the wad and propellant required for the round. It's reduced power makes it easier to use in the 25mm grenade, as the reduced performance allows it to be smaller and lighter weight than a traditional grenade. Approximately 30 can be carried for a pound, or for every 3 HE grenades that can be carried.

Rubber Rounds

Frag-12
The Frag-12 grenade is approximately 32 grams, around the same size as standard lead-shot, use a larger fin-stabilized explosive grenade designed as a smaller grenade



25mm Grenades
The standard cartridge of the 25mm is

High explosive dual-purpose air-bursting grenade

Thermobaric Grenade

Flashbang

Smoke Grenade