 The percussion cap helped lead to the self-contained cartridge, where the bullet is held in by the casing, the casing is filled with gunpowder and a primer is at the end.Joshua Shaw, an English-born American, is sometimes credited with the development of the first metallic percussion cap in 1814 but his claim remains clouded with controversy as he did not patent the idea until 1822.According to Lewis Winant, the US government's decision to award Shaw $25,000 as compensation for his invention was a mistake.