Can anybody describe the function of this German 20mm aircraft cannon round? The projectile is grey as is the fuse. It has traces of a red circle at tip of the fuse - see photo. I thought it might be a practice round with a dummy fuse but the fuse is ZZ1505 1942 with a waffenamt. Fuse seems to match the projectile - it doesn't look as if it's ever been taken off. Markings on projectile are unreadable.
Any help appreciated
Thanks