Geki-Karakuri: Double-Sear Matchlock Mechanism
Geki-karakuri are the most sophisticated Japanese matchlock mechanisms. Developed by Inoue Geki (d. 1646), a master gunner and gunsmith, these mechanisms used one or more coiled springs in addition to U-shaped mainsprings. Geki-karakuri locks were customizable, and the force required to pull the trigger could be set to several different levels. Unlike other mechanisms, geki-karakuri were virtually impossible to fire accidentally, but cocking the mechanism took more time.
Geki-karakuri locks were highly prized, but their many delicate components made them expensive to produce and finicky to maintain. As a result, they never fully replaced the simple hira-karakuri mechanisms that were used for most standard-issue military muskets.