The lock of a firearm is the mechanism used to initiate firing. It is generally used as a historical term, referring to such mechanisms used in muzzle-loading and early breech-loading firearms, as modern firearms uniformly fire by use of a firing pin to strike the rear of a cartridge. Side-lock refers to the type of construction in which the individual components of the mechanism are mounted on either side of a single plate. The assembly is then mounted to the stock on the side of the firearm. In modern firearm designs, the mechanism that initiates firing is generally built into the frame or receiver of the firearm and is referred to as the firing or trigger mechanism.
Hand cannon The hand cannon, which was the earliest of firearms, had arrived in Europe by c. 1338. These cannons were loaded from the muzzle. The propellant charge is lit through a touch hole. A small priming charge over the touch hole is ignited with a lit piece of slow match or similar. These hand cannons were ungainly: the difficulty being in holding and aiming the weapon while manipulating the slow-burning fuse needed to fire it. Improvements to the basic design placed the touch hole and a priming pan (flash pan) to the side of the barrel. A cover to the priming pan allowed this to be filled with priming powder in advance of firing, but there was no actual mechanism for firing.
Firelock A firelock is a firearm in which sparks ignite the priming. More specifically, it refers to the mechanism or lock of such firearms. It may also refer to a gun's lock that uses slow match to ignite the powder charge. The matchlock was a lever mechanism that simplified the ergonomics of firing. A slow match would be held clear of the flash pan in a spring-loaded pivoting arm (the serpentine). Depressing the firing lever would dip the burning match into the flash pan. The snap matchlock latched the serpentine back against spring tension. Actuating the trigger or firing lever would release the serpentine, allowing it to rotate and dip the lit match into the priming pan. This reduced hesitancy at the moment of firing, thereby improving accuracy. However, rather than firing, the match might be snuffed out when it struck the flash pan. The next advance was a self-igniting firearm that did not require a lit slow match to fire. The first of this type is the wheellock. The wheellock produces a spark in much the same way as a Zippo lighter. Pyrite held against a rotating steel wheel produces a spark directed at the priming charge in the flash pan. The wheel is rotated by a spring under tension. It would be wound up like a clock before each firing, held by a latch, and fired by a lever that released the latch. To avoid stalling, the pyrite would be lowered onto the rotating wheel rather than held against it permanently. The mechanism would also remove a cover from the flash pan at the moment of firing, sliding it forward. The cover would retain the priming charge in the flash pan during transit. The mechanism was altogether quite complicated, expensive and as a result found limited use.
The next advance in firearm design was the snaplock, which used flint striking steel to generate the spark. The flint is held in a rotating, spring-loaded arm called the cock. This is held cocked by a latch and released by a lever or trigger. The steel is curved and hinged. This accommodates the flint's arc, maintaining contact with the steel. The spark produced is directed downward into the flash pan. The snaphance incorporates a mechanism to slide the pan cover forward at the moment of firing. The doglock incorporates a second latch (or dog) as a safety mechanism that engages the cock in a halfway position, or half-cock. The dog is independent of the trigger. The dog is only released when the lock is brought to the full-cock position. The miquelet lock is the penultimate of the flint-sparking locks. It has an L-shaped frizzen, the base of which covers the flash pan and is hinged forward of the pan. The flint strikes against the upright of the "L" and flips the frizzen forward, revealing the pan to the sparks created. The miquelet lock also has a half-cock mechanism similar in function but differing in operation from the doglock. The flintlock is also referred to as the true flintlock to distinguish it from other flint-sparking mechanisms. It is also known as the French lock. It uses a frizzen similar to the miquelet lock and has a half-cock position. The distinction between the two locks is that the flintlock uses a single vertical sear to latch the cock in both the cocked and half-cocked positions. The sear is a lever that pivots in the vertical plane perpendicular 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 on 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.
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