The world’s smallest production firearm is the 2mm Kolibri (German for “hummingbird”), designed by a German watchmaker by the name of Franz Pfannl. About a thousand of these tiny pistols were made between about 1910 and the beginning of World War I in 1914 when production had to stop as the economy turned to a war footing.
The 2mm Kolibri is in all ways a standard firearm, but smaller. It uses the same simple blowback mechanism as many modern .22, .25, and .32 caliber guns, but is chambered for a proprietary (and now rare) 2.7mm centerfire cartridge. This cartridge fired a minuscule 3-grain bullet at 650 feet per second, giving it less muzzle energy than a typical airlift pellet. But because of its small surface area and high velocity, it should still be considered potentially dangerous. The gun was equipped with a six-round magazine and fired semiautomatically, with one shot per pull of the trigger until the magazine was emptied. Recoil was effectively nonexistent, given the minuscule size of the projectile.
How many Kolibri pistols were bought with the intention of actual self-defense is debatable, as the gun is far more of a novelty than a serious weapon. Still, it could have been seen as a legitimate deterrent against stray dogs—a common use for small firearms at the time. The sting of a Kolibri bullet could potentially frighten off a dog without subjecting the firer to the noise of a more typical firearm, or forcing them to carry something the size of a typical firearm (the Kolibri weighs just under 8 ounces).
Franz Pfannl would make several other unusually small firearms during his career, including 3mm and 4.25mm designs, but the kolibri pistol remains his most distinctive work.