When the Allied examined the weapons discovered in the German Reich after the war, they came across a device which was classified as a “spring gun” or “trip wire activated static defense machine gun”. Nevertheless, in actual fact it was a practice device with the name “Zielfeuergerät 38” (short “Zf.Ger.38”). For very realistically exercises on the training areas, it was necessary to create a well armed enemy. For this purpose the company C.G. Haenel from Suhl developed a blank-firing device in the German standard caliber 7.92 x 57 mm which could fire at the attacking soldiers…

For more details, see the full article on this by Michael Heidler:
https://www.forgottenweapons.com/light-machine-guns/zfg38-training-machine-gun/

Many thanks to the Royal Museum of the Armed Forces and Military History in Brussels for access to this very rare piece! Check them out here:
https://www.klm-mra.be/D7t/