A derringer is generally the smallest usable handgun of a given caliber. They were frequently used by women, because they are easily concealable in a purse or as a stocking gun. Such weapons designed specifically for women were called "muff pistols", due to their compact size enabling them to be carried in a muff. Derringers are not repeating firearms—repeating mechanisms such as those used in semi-automatic handguns and/or revolvers would add significant bulk to the gun, defeating the purpose The original cartridge derringers held only a single round, usually a pinfire or rimfire .40 caliber cartridge, with the barrel pivoted sideways on the frame to allow access to the breech for reloading. The famous Remington derringer design doubled the capacity, while maintaining the compact size, by adding a second barrel on top of the first and pivoting the barrels upwards to reload. Each barrel then held one round, and a cam on the hammer alternated between top and bottom barrels. The Remington derringer was in .41 Short caliber and achieved wide popularity. The .41 Short bullet moved very slowly, at about 425 feet per second (130 m/s), around half the speed of a modern .45 ACP. It could be seen in flight, but at very close range, such as at a casino or saloon card table, it could easily kill. The Remington derringer was sold from 1866 to 1935.