2 mm Kolibri

The 2 mm Kolibri (also known as the 2.7 mm Kolibri Car Pistol or 2.7x9 mm Kolibri) is the smallest commercially available centerfire cartridge, patented in 1910 and introduced in 1914 by Franz Pfannl, an Austrian watchmaker, with financial support from Georg Grabner. It was designed to accompany the Kolibri semi-auto pistol or single shot pistol, both marketed as a self-defense weapon.

Background
The cartridge weighed 5.3 grams (82 grains), measured 3 millimeters (0.12 in) at its widest point, and 11 mm (0.43 in) from the base of the primer to the tip of the bullet. The bullet itself weighed 3 grains (0.2 g), and was estimated to have a normal muzzle velocity of 650 feet per second (200 m/s), resulting in a muzzle energy less than 2 foot-pounds (4 joules).

The round was not accepted overly well. The 2 mm Kolibri's small size made handling and loading individual cartridges difficult, and the bullet itself was fairly weak, literature at the time suggesting the round was capable of penetrating only 0.5 to 1.5 inches (13 to 38 mm) of pine board. The round also suffered some accuracy issues, since the technology of the time was incapable of applying rifling to the bore of such a small caliber, resulting in no spin on the bullet.

The series, and most weapons by Franz Pfannl, were discontinued in 1938.

The cartridge (and related firearm series) is now a collector's item, with individual rounds going for over 70 United States dollars. Original guns for this round can sell for $5000 USD.