The ww2 Mills grenade could be used as a riflegrenade. The user had to screw a round base plate to the base plug. This way the grenade could be fired from the Cup Discharger with the use of a special cartridge. The grenade had to be fully inserted and the ring had to be pulled. The safety spoon was held in place by the discharger itself.

Shown above is the propelling cartridge as was used to fire most types of ww2 rifle grenades. Thanks Glenn!