# Mauser BK-27

The BK 27 (also BK27 or BK-27) (German abbreviation for Bordkanone, "on-board cannon") is a 27 mm (1.063 in) caliber revolver cannon manufactured by Mauser (now part of Rheinmetall) of Germany. It was developed in the late 1960s for the MRCA (Multi Role Combat Aircraft) program that ultimately became the Panavia Tornado.
The BK 27 is a gas-operated cannon firing a series of 27×145 mm cartridges with a typical projectile weight of 260 g (9.2 oz), and a total weight for the complete round of 516 g (1.14 lb). Most models use a linked feed system for the ammunition; however, the Eurofighter Typhoon makes use of a specially developed variant of the BK 27 that uses a linkless feed system instead, which is intended to improve reliability.

## Design

The Mauser BK 27 is used in the Panavia Tornado, the Alpha Jet, the JAS 39 Gripen, and the Eurofighter Typhoon. At one time Lockheed Martin was considering a licensed-built version for the F-35 Lightning II.
Rheinmetall has also developed remote-controlled naval versions, the MN 27 GS and the MLG 27 fully automatic naval guns, which are installed on many ships of the German Navy. Ninety-nine MLG 27s have been ordered by the German Navy so far. The cannon is a single-barrel, high-performance, breech-cylinder gun operated by a fully automatic, electrically fired, gas-operated system at a selective rate of 1000 or 1700 rounds per minute(+/− 100 rpm). The Mauser BK 27 utilizes pyrotechnic cocking charges to cycle the action.
The gun mainly fires mine shells as these have the best effect against aircraft, there are also several types of armor piercing shells like the frangible armour piercing shell named Fap 27 mm x 145 mm ammunition/peb327 (DM103).

### Operational history

In his book Typhoon, former RAF pilot Mike Sutton reported his 27 mm cannon jamming during a strafing run in Syria, against ISIS targets, while supporting Allied ground units. According to his book, the Typhoon was to be built, originally, without an internal gun, like the F-4 Phantom and the Harrier. However, while a decision was made to install an internal gun, this led to "manufacturing issues". Sutton claimed that during his strafing run the gun jammed after "twenty-six rounds", the HUD showing "GUN FAIL". During the debrief this problem was well known to both the pilots and ground crews. One pilot told Sutton: "They said that issue had been fixed", to which Sutton replied "Exactly. We've been here before."

## Operators
### Current operators
#### Algeria

    Algerian Navy

#### Austria

    Austrian Air Force:

#### Brazil

    Brazilian Air Force:
   * Saab JAS 39 Gripen E/F

#### Brunei

    Royal Brunei Navy
   * 4 × Darussalam class with 1 × MLG27 [de] each
   * 4 × Ijtihad class with 1 × MLG27 [de] each

#### Canada

    Discovery Air Defence Services:
   * Alpha Jet A (former Luftwaffe and QinetiQ Aircraft)

#### Czech Republic

    Czech Air Force:
   * Saab JAS 39 Gripen C/D

#### Germany

    German Air force:
   * Eurofighter Tranche 1
   * Eurofighter Tranche 2
   * Eurofighter Tranche 3
   * Eurofighter Tranche 4
   * Eurofighter ECR
   * Panavia Tornado IDS
   * Panavia Tornado ECR
    German Navy:
   * 4 × Brandenburg class (F123) with 2 × MLG27 [de] each
   * 3 × Sachsen class (F124) with 2 × MLG27 [de] each
   * 4 × Baden-Württemberg class (F125) with 2 × MLG27 [de] each
   * 6 × Niedersachsen class (F126) with 2 × MLG27-4.0 SeaSnake [de] each
   * 10 × Braunschweig class (K130) with 2 × MLG27 [de] each
   * 2 × Ensdorf class (Type 352) to be upgraded with 2 × MLG27 [de] each
   * 8 × Frankenthal class (Type 322) to be upgraded with 1 × MLG27 [de] each
   * 3 × Berlin class with 4 × MLG27 [de] each
   * 2 × Elbe class (Type 404) to be upgraded with 2 × MLG27 [de] each

#### Hungary

    Hungarian Air Force:
   * Saab JAS 39 Gripen C/D

#### Italy

    Italian Air force:
   * Eurofighter Tranche 1
   * Eurofighter Tranche 2
   * Eurofighter Tranche 3
   * Eurofighter Tranche 4
   * Panavia Tornado IDS
   * Panavia Tornado ECR

#### Oman

    Royal Air Force of Oman:
   * Eurofighter Tranche 3

#### Qatar

    Qatar Emiri Air Force:
   * Eurofighter Tranche 3

#### Saudi Arabia

    Royal Saudi Air Force:
   * Eurofighter Tranche 2
   * Eurofighter Tranche 3
   * Panavia Tornado IDS

#### South Africa

    South African Air Force:
   * Saab JAS 39 Gripen C/D

#### Spain

    Spanish Air Force:
   * Eurofighter Tranche 1
   * Eurofighter Tranche 2
   * Eurofighter Tranche 3
   * Eurofighter Tranche 4

#### Sweden

    Swedish Air Force (under the designation 27 mm akan m/85 / 27 mm automatkanon m/85)
   * Saab JAS 39 Gripen C/D and E/F

#### Thailand

    Royal Thai Air Force:
   * Alpha Jet A (former Luftwaffe aircraft)
   * Saab JAS 39 Gripen C/D

#### United Arab Emirates

    United Arab Emirates Navy:
   * 6 × Baynunah class with 2 × MLG27 [de] each

#### United Kingdom

    Royal Air Force:
   * Eurofighter Tranche 1
   * Eurofighter Tranche 2
   * Eurofighter Tranche 3

### Systems retired
#### Australia

    Royal Australian Air Force:
   * Alpha Jet A (former Luftwaffe aircraft, retired)

#### Germany

    German Air Force:
   * Alpha Jet A (retired and sold second-hand)
    Marineflieger:
   * Panavia Tornado IDS (retired and transferred to Luftwaffe)
    German Navy:
   * 8 × Bremen class (F122) with 2 × MLG27 [de] each

#### Portugal

    Portuguese Air Force:
   * Alpha Jet A (former Luftwaffe aircraft, retired in January 2018)

#### Saudi Arabia

    Royal Saudi Air Force:
   * Panavia Tornado ADV (retired in 2006)

#### Sweden

    Swedish Air Force:
   * Saab JAS 39 Gripen A/B

#### United Kingdom

    Royal Air Force:
   * Panavia Tornado IDS
   * Panavia Tornado ADV
    QinetiQ:
   * Alpha Jet A (former Luftwaffe aircraft, retired in January 2018)

## Specifications

Data from Jane's Information Group
* Type: single-barrel, five chamber revolver cannon
* Caliber: 27 mm × 145 (1.063 in)
* Operation: revolver
* Length: 2.31 m (7 ft 7 in)
* Weight (complete): 100 kg (220 lb)
* Rate of fire: 1,000-1,700 rpm selectable (+/− 100 rpm)
* Muzzle velocity: 1,100 m/s (3,600 ft/s)
* Muzzle energy: ≈157,300 Joules
* Projectile weight: 260 g (9.2 oz)