Wikipedia
The Minengeschoss ('mine-shell') was a high-capacity autocannon ammunition originally developed in Germany and used in the Luftwaffe's larger caliber aircraft armament during World War II. This new type of high-explosive shell differed from conventional H.E. ammunition in that it had much thinner walls. The shell was drawn from high-quality steel, instead of having the explosives cavity drilled into a solid shot, which allowed thinner-wall construction and therefore a far greater amount of explosive filler.
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.