Coming in at just 5.3 grams, the 2.7x9mm Kolibri cartridge is the smallest commercially available centerfire round in the world. That makes the only gun that shoots it, the 2.7mm Kolibri Car Pistol, the smallest commercially available semiauto in the world.
This thing is downright minuscule. It is also very, very expensive. Due to the discontinuation of the round and high demand from collectors, a single cartridge can cost well over $70. As for the handgun itself, bidding starts at $5,000.
Ian from Forgotten Weapons explains just about everything you need to know about this tiny pocket pistol.