to the axis of rotation of the cock and acts much like a pawl engaging the catch points of a ratchet gear. The tumbler is similar in function to a ratchet gear. It is mounted on the inside of the lock-plate and has two catch-points corresponding to the half-cocked and full-cocked positions. The half-cock catch-point is a V-notch into which the sear fits and cannot be levered away by the trigger to disengage the tumbler. Firelock firing mechanisms are assembled either side of a mounting plate. The assembly is then mounted to the side of the stock of the firearm. The actual trigger may be separately mounted from the lock-plate. Side lock refers to lock mechanisms of this general construction. It continued to be used in percussion-lock firearms and early firearm designs using metallic cartridges. Percussion lock The advent of the percussive ignition eliminated the need for a spark to discharge a firearm. Instead, the discharge is initiated by striking a shock-sensitive explosive material. Initial patents are attributed to the Reverend Alexander John Forsyth, who use a fulminate powder delivered from a charger that was integral to the lock mechanism. The charger contained a firing pin that was struck and in turn, struck the fulminate. The mechanism was otherwise constructed similar to that of the flintlock. The fulminate used in percussive locks was variously packaged as pills, metal tubes and paper patches but the percussion cap soon predominated. The flintlock mechanism was readily adapted to utilise this new technology. The flash pan was removed. A nipple (a small hollow cone) was fitted to the touchhole. The percussion cap is fitted over the end of the nipple. The cock was modified to strike the cap and redesignated as the hammer. As a safety measure, the face of the hammer was soon hollowed to surround the cap. As an economy, many existing flintlocks (particularly military stocks) were converted to use the percussion cap. Most conversions modified rather than replaced the lock mechanism of the firearm being converted while lock designs in new models of longarms were largely unchanged. Some designs emerged, such as Maynard carbine and the pellet feed system employed by the Sharps carbine, which mechanised the recharging of the primer but such systems were never widely adopted. Percussion lock refers generally to firearms that use external percussive primers. Cap lock and tube lock refer to percussion-lock firearms that utilised either