hello together,
the cartridge cases were caught in a case bag on the plane.
in german it is called "hülsenfangsack" ...
see figure #2 or #6 (the newer one) at the picture below.
source:
http://www.luftarchiv.de/index.htm?/...ate/waffen.htm (in german only)
maybe some of the cases got lost of them!?
best regards
ghost