Mine shell (projectile)
A mine shell (directly translated from the german term minengeschoss) is an ammunition type consisting of a very high-capacity high-explosive shell. The type was originally developed in Nazi Germany during WW2 to increase the effectiveness of the Luftwaffe's aircraft guns.
The word mine in the name mine shell does not refer to the common use of the word as in a land mines or naval mines. It is an ammunition term used in several Germanic languages meaning explosion with minimal fragmentation effect or maximum explosive effect. In other words, the explosion itself is meant to do the majority of the damage to the target.
Construction & effectEdit
A mine shell differs from conventional high explosive rounds in that it has much thinner walls which allows for more explosive content. This gives the shell a much bigger explosion at the expense of shrapnel. Beyond impact effect mine shells have different weight properties compared to regular high explosive shells. Explosive filler is lighter than metal which makes the projectiles a lot lighter which in turn gives them higher muzzle velocity compared to heavier shells. A disadvantage is that the same lower mass reduces range as the projectile has correspondingly less momentum.
The type was developed in Nazi Germany at the end of the 1930's due to problematic trials with the 20 mm MG FF cannon. Its conventional high explosive rounds didn't have satisfactory results against aircraft as the fragments had insufficient effect on construction integrity or control surfaces compared to the actual explosion. As a result of these trials, the German ministry of air defense "Reichsluftministerium", or "RLM" for short, ordered a development of new 20 mm cannon shell in 1937 which should have increased explosive force at the expense of impact and fragmentation effect.
Conventional explosive ammunition was made by drilling the explosive cavity into a solid steel shot, a design which due to the massive impact and structural integrity of such a round, made sense when seeking to penetrate hard targets. By contrast, aircraft are lightly constructed and overall relatively soft targets, and unless they struck hard areas such as engines or armour such shells tended to punch through their structure rather than transfer their kinetic force to it - which meant that such a massive impact was to some degree superfluous. It could also even be conducive to over-penetration, where a shell passes through the target before exploding. German ordinance engineers therefore took a new approach, and designed a round made from drawing steel into a suitable shape, giving thinner-wall construction and therefore space for a far greater amount of explosive filler than previously. The metal also had to be high-quality steel to keep the structural integrity. The new ammunition type was given the designation Minengeschoss, German for 'mine-shell,' due to the larger explosives payload.
The new invention was highly successful. It was, indeed, less effective at penetrating deep into target aircraft or breaching their internal armour than the conventional rounds used by the Allies in WW II, but the power of the explosions inflicted serious damage wherever they occurred within the structure of the plane, rendering these apparent disadvantages less relevant.
As well as creating larger explosions this new ammunition type also came with another desirable trait. Explosive matter is a lot lighter than steel, which gave this new ammunition type a low weight and thus, for an equal amount of propellant, correspondingly higher velocity. Like the greater explosive payload this was also a big advantage, as air combat involves shooting at fast-moving targets.
Conversely and equally significantly, another way the Luftwaffe benefitted from the new ammunition's lower weight was that when they deployed small, light guns only capable of firing low-powered propellant cartridges they could still achieve useful velocities, and this, in combination with the larger explosive warhead gave such weapons a much greater effect than they could have had firing conventional rounds. Examples are the 20mm MG FF/M (The Minengeschoss-firing version of the MG FF), well-suited to mounting in the wings of the Luftwaffe's light and compact Bf 109 fighters, and 30mm MK 108. Both weapons were highly militarily significant, the first during some early stages of the conflict, the latter during the second half.
Unfortunately for the Reich, one disadvantage of Minengeschoss shells is that the lower momentum of the lighter round also caused it to lose its velocity relatively quickly; they adopted a partial solution to this shortcoming when it came to 30mm caliber shells by introducing a more streamlined type, the Ausf.C, which overcame air resistance more effectively - albeit at the loss of a little explosives capacity.
As volume increases with the square of the radius of a cylinder, and as autocannon shells are close to cylindrical in shape, the advantages of low weight and high explosive payload furnished by the Minengeschoss approach were particularly manifest in large calibre weapons such as the 30mm MK 108, which were used with devastating results on allied bombers in the later air campaigns of the war in Europe.
Minengeschoss ammunition was first fired in combat from the MG FF/M during the Battle of Britain in 1940 by the Luftwaffe's Bf 109E and Bf 110C fighters. Subsequently it was used in the Luftwaffe's standard 20mm gun, the MG 151/20 cannon, one of the best 20mm air-to-air guns of WW II,  and in the high-velocity 30 mm MK 103, amongst others.
To give some impression of the actual difference in payloads between these shells: the 20 mm M-Geschoss shell (used in MG 151/20 and MG-FF/M cannons - the same shell was used in both cartridges) had an 18 g HE filling while the typical filler load in conventional 20 mm shells at the time was 6 to 10 g.
In 30 mm caliber different M-Geschoss designs were available: the original blunt-nosed Ausf.A had an 85 g filling of nitropenta (PETN), which was reduced to 72 g in the more streamlined Ausf.C shell (the "missing" B was a practice shell). In comparison, the PGU-13/B HEI round for the GAU-8/A Avenger gun of the A-10 Warthog contains only a 58 g explosive filler, while the 30 mm OFZ shell of Russian GSh-301 and GSh-30-6 cannons has a 48.5 g filler.
After the defeat of Germany in World War II, several countries started using the design for their own post-war aircraft armament, for example in the HE shells of Britain's ADEN cannon and the French DEFA 540. The guns themselves were developments of the German Mauser MG 213.
Sweden developed several different mine shells in several different calibers after the war. Some examples being a mine shell variant for the 20 x 110 Hispano cartridge and one for the 57 x 230R Bofors cartridge.
- "Shell types: Minengeschoß".
- Williams and Gustin 2003
- Forsyth 1996, p. 168
- Note: The information in Forsyth 1996 is on the design and construction of the MK 108 and the relevant Minengeschoss.
- Beskrivning över 20 mm AKAN m/49. Stockholm: KFF förlag. 1955. Sweden. 1955.
- Flyghistorisk revy nummer 31, SAAB 18. Sweden: The Swedish air historical society. 1984. p. 76.
- "Gripens vapen (the weapons of the Griffon) pdf" (PDF).