Parallel developments

Joshua Shaw is sometimes credited (primarily by himself) with the development of the first metallic percussion cap in 1814, a reusable one made of iron, then a disposable pewter one in 1815 and finally a copper one in 1816. There is no independent proof of this since Shaw was advised he could not patent it due to Alexander Forsyth's patent for using fulminates to ignite guns being in force between 1807 and 1821. Shaw says he only shared the development of his innovation with