This pistol belonged to a member of EOKA, a group who fought against the British and Turkish for Cypriot independence during the 1950’s.
The barrel on the pistol is a 20mm cartridge case! I think the general idea was to pack a very small charge of blackpowder at the back of the “barrel” by the touch hole and jam some sort of projectile in the front, sort of like a blackpowder cannon. As the text in the above photo says, it would have need to be held right up to the victims head.
I do wonder if it was ever fired because a cartridge case is not designed to hold up against pressure, it is designed to expand. I suspect this would do as much, if not more, damage to the operator than it would to the intended target.
Hat Tip: weissent @ MP.net