Most cannon shells were made by drilling a hole through a solid steel projectile, to make room for the chemical contents. This led to heavy, thick-walled shells which only contained around 8-10% HEI by weight. In a typical 20mm shell weighing 120g, this meant that only around 10g was HEI mixture. The Germans developed a new type of shell made by drawing from a disk of steel, just as cartridge cases are made. These projectiles were thin-walled and much lighter overall, yet had far more room for chemicals. Their large capacity led to them being called "mine shells", or Minengeschoss (M-Geschoss for short). The standard 20mm M-Geschoss weighed only 92g yet held 18-20g of HEI chemicals, doubling the blast/incendiary effect. It was not always better than the traditional heavy shell (it depended on where it hit) but was usually more effective. An additional benefit was that the light weight permitted a higher muzzle velocity, reducing the time of flight.
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