caplock
A firelock mechanism where a hammer strikes a percussion cap lined with filament mercury, which ignites and sends flame into the barrel, setting off the gunpowder inside. Was much more reliable than the flintlock, which it replaced, but it was replaced in turn just half a century later by the advent of self-contained cartridges, which eliminated the need for an external lock system altogether.
The time period for the use of caplocks is almost exclusively the mid-19th Century: the Mexican-American War, Crimean War, American Civil War, and Boshin War. Though some caplocks would continue to be used in the American West, most would be converted by various methods to use cartridges.