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The Percussion System  180. Invention and Development 180.3 Firearms mechanical ignition systems invented and used from the 16th century depended on a spark generated by the scraping of a rock, such as flint or pyrites, against steel, to ignite a priming charge that, in turn, ignited the main charge. The flintlock had been the primary ignition system of military shoulder arms throughout the 18th century. Although this system was vastly superior to its predecessors, it had several weaknesses apparent in its use in military arms. These weaknesses included the limited availability of high-quality flint rock, or of artisans capable of splitting and chipping it into the proper sizes and shapes for use in various arms.1 Also, the sharp front edge of the flint rapidly wore down in protracted firing, diminishing the number of sparks produced to ignite the priming charge. The wear caused the shooter either to need to replace the flint with a new one or to temporarily renew the edge by skillful tapping of the worn front edge with a hammer-like instrument, chipping off some small pieces. It has been reported that, in combat, military flintlocks commonly failed to fire about one-quarter to one-third of the time. Another weakness of the system was the priming powder receptacle. This receptacle, or pan, had a hinged cover that kept the priming powder inside until the weapon was fired. However, it often failed to prevent the entry of moisture to the priming, which made the arm almost useless in the rain or even heavy fog. Military flintlocks usually had to be fired with the locks somewhere near the vertical position; these arms could not be fired upside down, because the priming powder fell out when the flint began its scraping action on the frizzen. Towards the end of the flintlock period, some high-quality commercial flintlocks made in England, France, and the United States had frizzens and pans of superior “waterproof” design; these elements components were painstakingly fit together so they would not admit moisture and could be fired in almost any position. This level of craftsmanship was simply not feasible in the large-scale production of military arms at national manufactories and under government contract, however. In the flintlock system, there is a delay between the pulling of the trigger and the ignition of the main charge. A few tenths of a second are required for the sparks to ignite the priming powder that, in turn, ignites the main charge. The duration of this delay could be extended by even a small amount of moisture in either the priming or main charge, or by residue from previous firings. The 1 This is called “knapping.” The Percussion System xxx ignition of the priming charge produced a flash and puff of smoke that, in shoulder arms, was just a few inches from the shooter’s face, and immediately to the right of his line of sight along the top of the barrel. This, and the ignition delay, exacerbated the shooter’s natural tendency to flinch; the infantryman and rifleman had to be trained to hold the arm steady through this delayed ignition. The percussion ignition system either greatly reduced or eliminated these weaknesses of the flintlock system. As the name suggests, the spark that ignites the main charge is generated by the hammer, either directly or indirectly, sharply striking a chemical compound that has the capacity of detonating when so struck. By 1800, several compounds had been discovered that were capable of violent explosion when struck. A French scientist named Claude-Louis Berthollet had experimented with compounds containing potassium chlorate, fulminate of mercury, and fulminate of silver with the goal of finding a new form of gun powder. He abandoned his research when he learned that the explosions generated by these compounds were too powerful. Scottish clergyman Alexander John Forsyth was also an amateur chemist. He experimented with similar compounds as early as 1793. His research differed from that of others: it was not to find a substitute for gunpowder, but to find a better system of igniting the main gunpowder charge in the barrel. He invented what is commonly referred to as the “scent bottle” lock and received a patent for this ignition system in the United Kingdom on April 11, 1807. Its salient feature was a rotating scent bottle–style reservoir for a fulminate of mercury compound. When rotated 180 degrees from the firing position, it deposited a minute amount of this compound...

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