In 1920, Fritz Mann of Germany patented the idea of cutting a shallow ring in the chamber of a pistol as a delaying mechanism. When fired, a cartridge case would expand into this groove, thus requiring more time and energy to push the case out of the chamber and effectively delaying opening. This allowed Mann to reduce the weight of the operating parts of his model 1920 semiauto pistol in .25ACP (aka 6.35mm Browning). The gun was designed to be as small and as light as possible; a true pocket pistol. Thousands of them were made in 1920 and 1921, although he gun failed to see long-term popularity.