This weapon is a 27×145mm caliber fully automatic gas-operated single barrel revolver gun with a five chamber breech cylinder. It has a barrel length of 1.40 meter and an overall length of 2.31 m.
It was developed for use in the Panavia Tornado aircraft in 1977 by German Mauser-Werke Oberndorf Waffensysteme GmbH and Oerlikon Contraves Pyrotec AG. Besides the Tornado, it is also used in the Swedish Gripen and as a blister pod in the Alpha Jet. An evolved version is used in the Eurofighter Typhoon, and finally a naval version is produced as well. At present it is estimated that more than 3000 BK 27s are in service around the world.
The cannon is relatively lightweight at only around 100 kg including barrel, but with a natural rate of fire of approximately 1700 rounds per minute (instantaneous time to rate), the relatively large shell (260g) and the high muzzle velocity of just over 1 km/s (v0) it packs a punch. In comparison, the seasoned M61 Vulcan Gatling-type cannon carried by most U.S. fighters have a much higher rate of fire, but because of the Vulcan's smaller shell (20 mm) and its slower time to rate, the BK 27 is able to throw more weight towards the target when fired in bursts than the Vulcan.
The cartridge is ignited electrically and fed to the cylinder either through linked belts or, in the case of the Eurofighter, through a linkless conveyor belt ammunition feed system, the first such system for revolver guns. Linkless systems (which are a staple in modern Gatling-type cannons) are less prone to stoppage and the ammunition uses considerably less space. Still, the system isn't designed for magazines with more than 200 rounds.
A wide variety of ammunition is available for the BK 27, ranging from armor piercing SABOT rounds to high explosive and incendiary shells. The different types of ammunition all have the same internal and external ballistic properties allowing for the use of belts with mixed ammunition for greater flexibility, as on the Tornado, without the need to recalibrate sights.
This weapon is not about to outcompete the massive 30mm GAU-8 Avenger cannon, but in a world where the doctrines are again swinging towards the no-gun fighter aircraft the Mauser's low cost and small size arguably makes it the most likely to fit the bill of the aircraft designers and top brass.