MK 108 cannon
| MK 108 | |
|---|---|
API Blowback | |
| Rate of fire | 650 rounds/min MK 108A: 850 rounds/min[citation needed] |
| Muzzle velocity | 540 m/s (1,770 ft/s) |
The MK 108 (German: Maschinenkanone—"machine cannon") is a 30 mm caliber autocannon manufactured in Germany during World War II by Rheinmetall‑Borsig for use in aircraft.[1]
The cannon saw widespread use as an anti-bomber weapon during the second half of the war, first seen in 1943 in the Bf 110G-2 bomber destroyers and Bf 109G-6/U4.[1]
Four MK 108's formed the main armament of the Me 262 the next year.[2] It could be found on some versions or optional mountings on practically every other German fighter of the era.[citation needed]
Development
The weapon was developed as a private venture by the company in 1940 and was submitted to the
The MK 108 was quickly ordered into production and was installed in a variety of Luftwaffe fighter aircraft. It saw first operational service in summer 1943 with the Bf 110G-2 bomber destroyers and in the Bf 109G-6/U4.[3]
Design details
Ammunition
The cannon used specially-developed 30×90RB mm ammunition—30 mm calibre, 90 mm case length,
This resulted in a shell with a thin but strong wall, which hence had a much larger cavity in which to pack a much larger explosive or incendiary charge than was otherwise possible.[citation needed]
Construction
The cannon proved to be relatively light, effective, reliable, compact and easy to manufacture due to its simple construction—80% of the weapon was made from stamped parts, and the number of moving parts was kept to a minimum by using advanced primer ignition blowback (APIB) operation. The simplicity of construction allowed inexperienced workers to make the parts (mostly women).[4]
The MK 108 was optimized for a high rate of fire at the expense of ballistic performance.[citation needed]
It was easy to maintain, and its compact size, low weight and electrical priming made it ideal for aircraft installation. [citation needed]
The cannon's distinctive heavy pounding sound and high rate of fire gave it the nickname "pneumatic hammer"[1] amongst Allied aircrews, who feared its destructive power.
Mechanism
Normally, gas-operated or recoil-operated mechanisms are used in automatic weapons of rifle calibre and larger because the chamber pressure in such weapons is very high. Therefore, if a simple blowback system (where there is no positive lock between the bolt and barrel) is used, the bolt may recoil and open the breech while the chamber pressure is still high, causing damage to the weapon and split cases (see blowback article for more information). To avoid this, simple blowback guns have to use low-powered cartridges or a very heavy bolt.[citation needed]
In an Advanced Primer Ignition Blowback design such as the MK 108, the forward motion of the bolt is used instead of a locking mechanism to prevent this premature opening. When the 108 is ready to fire, the bolt and main spring are held back at the rear of the gun, the spring under considerable tension. When the trigger is squeezed, they are released and shoot forward at a high speed. The bolt picks up a cartridge and chambers it, but instead of coming to rest against the breech face, it follows the case a small distance into the chamber—which is of course made specially longer in these guns to accommodate this manoeuvre.
Primer ignition is timed so that the bolt is still moving forward when the propellant is ignited. The expanding gases from the fired round stop the forward motion of the bolt, then reverse its motion. The key characteristic of the APIB system is that, because the resistance due to the weight of the bolt and the mainspring are supplemented by the bolt's considerable forward momentum, the propellant gases are contained in the barrel for critical microseconds, and the projectile will have had time to leave the muzzle, allowing the gas to escape forward and reducing the chamber pressure to a safe level before the bolt and cartridge case emerge from the opposite end.[6] Once they emerge the weapon cycles like other automatic guns, with one significant exception: instead of simply ejecting the spent cartridge case, the 108 reinserts it into the empty link in the ammunition belt. The heavy bolt continues backwards, compressing the main spring. When the spring is fully compressed it begins to expand forwards again, reversing the motion of the bolt and recommencing the cycle. This sequence is repeated until the trigger is released or the ammunition is exhausted.[5]
The APIB design makes practical the use of far more powerful ammunition than with simple blowback operation, but the length and the speed of the bolt's movement within the chamber are limited by the stresses placed on the case by the sliding motion, which takes place under high gas pressure. To keep these within limits either the bolt must be heavy to absorb the pressure, or the barrel must be short to limit the duration of high pressure within the barrel.[5] The operational tradeoff is that a heavy bolt reduces the rate of fire while a short barrel reduces ballistic performance.[citation needed] The designers of the MK 108 opted for a high rate of fire and thus used a relatively light bolt, accepting reduced ballistic performance due to the corresponding necessity of a short barrel. As a result, the MK 108 had a muzzle velocity of only 540 m/s,[1] compared to the approx. 800 m/s for the MG 151/20.[7]
Another significant feature is that, in the APIB system the cycle starts with the bolt open, which prevents an autocannon using the APIB principle from being accurately synchronized with an aircraft's propeller.[6]
- MK 108 bolt cycle
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- MK 108 feed cycle
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Operational usage
The MK 108 saw widespread use among fighters tasked with shooting down enemy bombers. Some of the aircraft deploying, or intended to be armed with, the MK 108 were
The MK 108 was also fitted to
Related designs
| MK 112 | |
|---|---|
| Production history | |
| Designer | API Blowback |
| Rate of fire | 300 rounds/min |
| Muzzle velocity | 594 m/s (1,950 ft/s) |
The MK 108 mechanism was scaled up in the MK 112 cannon, using a 55×175RB cartridge. The MK 112 was intended to be fitted in pairs in the nose of Me 262 fighters, with 25 rounds per gun, and also in the nose of later models of the
See also
References
- ^ ISBN 978-0-7864-5280-4.
- ISBN 978-1-4728-5053-9.
- ^ Messerschmitt Bf 109 F,G, & K Series by Jochen Prien, Peter Rodeike page 108.
- ^ ISBN 978-1-5267-8524-4.
- ^ a b c Armor. U.S. Armor Association. 1994.
- ^ ISBN 978-1-78500-921-1.
- ISBN 978-1-4728-4630-3.
- ISBN 978-1-5267-1055-0.
- ISBN 978-1-4728-3868-1.
- ISBN 978-1-62788-495-2.
- ISBN 978-1-78096-686-1.
- ^ ISBN 978-2-37297-325-0.
- ^ ISBN 978-1-291-29268-8.
- ISBN 978-0-7603-4398-2.
- ^ Metzmacher, Andreas (2 December 2021). Gotha Aircraft: From the London Bomber to the Flying Wing Jet Fighter. Fonthill Media.
- ISBN 978-1-4728-3636-6.
- ^ ISBN 978-1-84037-435-3.
- George Chinn1951, The Machine Gun: Development During World War II and Korean Conflict by the United States and their Allies of Full Automatic Machine Gun Systems and High Rate of Fire Power Driven Cannon, Volume III, Parts VIII and IX., p. 627
External links
- MK 108 ammunition types
- World War 2 Fighter gun effectiveness comparison Archived 30 October 2017 at the Wayback Machine
- factsheet from the National Museum of the United States Air Force, Dayton, Ohio
- German language page on the MK 108 autocannon
