Be aware that before WWII the .22 Hornet was not known in Germany.
What was widely used however was the 5,6x35R Vierling which is basically the .22 WCF with a smokeless and hotter load.
The 1940 RWS Handbook says: bullet of 2,55 g, muzzle velocity of 800 m/s from a 60 cm barrel, pressure 2400 at.

The modern RWS / DN book says Hornet cases need some work: sizing, trimming, maybe the rim must be made thinner. And it say a 40 grain .222 Hornady bullet made for the .22 Jet should be used.

Regards,
fuhrmann