Paatz was a gunmaking family from the late 1800s. did not survive WW 2. They were near Suhl where EVERBODY was a gunmaker.
POSSIBLY a .22 LR (look for 5.4 as metric designation) but Paatz also made Flobert short range target guns, could be a BB cap firearm.
From the left, the really short round is a CB cap, the one to its right is a BB cap.