Your specimen is only the upper part of a 30 mm German Antitank Rifle grenade known as Gewehr Panzergranate 30. This part is now empty, it contained a shaped load of Tolite just atop of a disc of priming compound.made of wax-phlegmatised Nitropenta.
This upper part should be screwed in the missing grenade rear part, or “tail”, with has two axial cavities, containing the detonator (a cylindric aluminium container known as kleine Zundladung 34 ), a striker and an inertial armament system, activated when the round is fired from the Schiessbecher (grenade cup).
There are two types of launching cartridge, Gewehrkartusche f
Philippe, thank you very much!!!
Yuri, here’s a picture of a complete grenade, from “Second World War Combat Weapons: Vol 1” (Hoffschmidt and Tantum);