I'm sure military veteran readers will remember recoilless rifles such as the US M18 57mm., M20 75mm., M67 90mm. and M40 105mm. weapons (six of the latter being mounted together on the famous M50 Ontos); the Swedish Carl Gustav 84mm. (still in front-line service today, in upgraded form); and the British Wombat 120mm. Despite being called 'rifles', they were actually small artillery pieces. The Soviet Union developed its own equivalents.
Most such weapons have fallen into disuse with the development of guided missiles, but now comes news that a modern version of a recoilless rifle - actually semi-recoilless, if I understand the article correctly - is under consideration for use aboard lighter armored vehicles.
This technology is called RAVEN, which stands for Rarefaction Wave Gun.
The operating principle behind RAVEN is similar to older recoilless guns, in that a limited amount of propellant gas is vented backwards in order to mitigate the recoil force of shooting a projectile. However, unlike recoilless guns, which lose velocity relative to conventional guns, RAVEN guns retain the same velocity and power as a conventional gun while reducing recoil forces and erosion to the gun. This makes this ideal for light vehicles, as the cannon itself can be made from lighter materials, and the vehicle does not need to “dig in” with a spade to stabilize itself before firing.
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Unlike earlier recoilless guns, the chamber in which the propellant and cartridge is placed is sealed at the beginning of the combustion cycle. After ignition, but before the projectile has reached the end of the barrel, the combustion chamber opens and starts venting gas. This venting of the gas gives RAVEN guns their recoilless properties, as the mass of gas leaving the gun by moving backwards compensates for the mass of the projectile moving forwards. This venting of the gas creates a drop in pressure, which then propagates down the gun barrel. This is the eponymous rarefaction wave. The wave then helps propel the projectile down the barrel, allowing it to leave without any loss in velocity. The early venting of the gas means that the materials that comprise the gun heat up less, allowing the gun to fire faster without overheating. This synergizes with the possibility to make guns of a lower weight, due to the recoil reduction granted by RAVEN technology.
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Overall, RAVEN guns present an interesting, high-caliber armament option that could provide America’s next generation of light vehicles the firepower they need to overmatch any current and future threat. While the technology is not yet mature, it is based squarely on concepts already understood and developed.
There's more at the link.
It appears that 35mm., 45mm. and 105mm. versions of the RAVEN cannon have already been successfully tested, and further development is ongoing. The 105mm. version is illustrated below (click the image for a larger view).
If the technology can be perfected, we may yet see a ballistic equivalent to the M1 Abrams' 120mm. cannon, mounted on a platform weighing half as much, and much more mobile. That would please organizations like the US Marine Corps, as it would be easier to land lighter vehicles like that from the sea, if necessary.