2 mm Kolibri

The 2 mm Kolibri (also known as the 2.7 mm Kolibri Car Pistol or 2.7×9 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.

The name is derived from the Kolibri or Hummingbird, which is among the smallest of birds.

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 cartridge headspaced on the mouth of the case. The bullet itself weighed 0.2 g (3 grains), and was estimated to have a normal muzzle velocity of 200 m/s (650 fps), resulting in a muzzle energy 4.0 joules (3 foot-pounds).

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 10–40 mm (0.4 to 1.6 inches) 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 US$70. Original guns for this round can sell for US$5,000.