It's 35x228R training ammo. Fired by the Oerlikon KD and 35/1000 series high-volume automatic guns, the Bushmaster III chain gun and the prototype Rheinmetall Rh503.
As far as systems go, these guns are used in:
- all G D F series anti-aircraft guns (aka Skyguard and Skyshield) (using KDA, KDB or 35/1000 guns)
- the G D M series naval turrets (aka Millenium and OTO Melara GDM-A/-C) (using 35/1000 or KDA/KDC)
- the Marksman SPAAG turret series (using KDA guns)
- other vehicles: Gepard SPAAG (KDA), CV9035 IFV (Bushmaster III), Marder 2 IFV prototype (Rh503)
Edit: G D F spaced. For whatever reason the forum software censors the word otherwise.