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 doesn't refer to the common use of the word like land mine s or the naval mine s. It's an ammunition term used in several Germanic languages meaning explosion with minimal shrapnel effect or maximum explosive effect. In other words the explosion is meant to do the majority of the damage to the target.

Construction & effect
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, although it does limit their range due to the lesser amount of kinetic energy. But this is generally not a problem since most mine shells has a time fuse which detonates the shell after a certain amount of time to not become UXO.

History
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 fragmentation effect.

As a result of this the new shell type had to be cast to allow thinner-wall construction and therefore a far greater amount of explosive filler. The metal also had to be high-quality steel to keep the structural integrity. Previous explosive ammunition where made of common steel and had the explosive cavity milled into a solid steel shot which limited the size to not effect the structural integrity.

The new ammunition type for the designation Minengeschoss which basically means that it is an explosive projectile meant to mainly do damage through the primary explosion and not with fragmentation.

Beyond greater damage against aircraft this new ammunition type also came with some other desirable traits. Explosive matter is a lot lighter than steel which gave this new ammunition type a low-weight which correspondingly gave it higher velocity. Like the greater explosive payload this was also a very desirable characteristic, as air combat involves shooting at fast-moving targets; although less desirably, the same low mass and therefore low momentum caused the Minengeschoss to lose its high velocity relatively quickly.

It was used, amongst others, in the Luftwaffe's 20 mm MG FF/M and MG 151/20 cannon, and the 30 mm MK 103 and MK 108 cannon. It was first used in combat during the Battle of Britain in 1940 by the Luftwaffe's Bf 109E and Bf 110C fighters. 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 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.

Post-war use
After the defeat of Germany in World War II, several countries started using the design and used it 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.

The type is still used today in autocannons such as the Mauser BK-27.