.41 short

The .41 Rimfire Cartridge was first introduced by the National Arms Company in 1863 and was also known as the .41 Short and the .41-100. In most designations like this, the second number refers to the black powder load, though in this case it means "41 hundredths of an inch".The .41 Short was created with the intention that it be used in a small, single-shot derringer, which likely is the reason for the very low ballistics (most derringers were and are chambered for cartridges that were not originally intended to be used in such a small weapon). Remington Arms began producing their famous Remington Model 95 over/under double barrel derringer chambered for the .41 Rimfire cartridge in 1866.
In 1873 the slightly more powerful .41 Long (rimfire) and the .41 short Colt (central fire) was introduced in the Colt New Line pocket revolver.

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