While interned in a POW camp during WWI Louis Marquis designed a .22 belt buckle gun. He later received a patent the design and during WWII was commissioned by Himmler to produce prototypes. It is thought that about 12 were made.
During the 50s and 60s many copies were made in German machine shops, possibly to cash in on the rarity of the originals.
[ Many thanks to Sven (Defense and Freedom) for emailing me the the info. ]