The 2.7mm Kolibri (2.7x9mm) is a Austro-Hungarian small centerfire pistol case.
The 2.7mm Kolibri was marketed alongside the Kolibri pistols. It was developed in 1914 by Franz Pfannl, an Austrian watchmaker, with financial support from George Grabner. The 2.7mm Kolibri round was not well accepted due to a variety of reasons; the bullet's small size made loading cartridges into the magazine difficult, the bullet was very underpowered, and very innacurate among other reasons.
One bullet weighs just 0.2 grams (0.007 ounces or 0.0004 pounds), and is headspaced on the mouth of the case. It is the smallest commercially available cartridge, and the smallest known weapon cartridge to date. Due to its extremely weak stopping power, it is considered obsolete. In spite of that, the cartridge and the related pistol are considered collector's items.
The bullet, when fired, has a normal muzzle velocity of 200 meters per second (656.2 feet per second), which resulted in a rather pathetic muzzle energy of 4 joules (0.96 calories).