The original derringer pistol was a single-shot muzzle-loading pistol.A derringer is generally the smallest usable handgun of a given caliber.They were frequently used by women because they are small and easy to conceal in purse.
Derringers are not repeating firearms - repeating mechanisms such as used in semi-automatic handguns 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 the top and bottom barrels.The Remington derringer was in .41 rimfire caliber and achieved wide popularity.The .41 rimfire bullet move very slowly at about 425 feet per second,a modern 45 ACP travel at 850 feet per second.
Some favor the derringer as a concealed carry weapon because of its size as well as the swiftness of putting it into action.Critics believe it is not an adequate weapon for self defense since derringer possesses a two-shot capacity.