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For maximum efficiency and effectiveness, a primer must offer the precise heat that a particular propellant load needs. Bulky, slow-burning powders for instance require a specific type of flame to ignite and burn properly. Too much heat and flame unnecessarily raise early chamber pressure, thereby “pushing the cycle.” Insufficient heat and flame do not ignite a large enough portion of the propellant for pressure to rise sufficiently before the chamber is decompressed by the load’s movement and the decreasing confinement.

The story of the primer began in about 1807 when Scottish hunter and inventor A. J. Forsyth discovered that a particular mixture of chemicals produced an explosion when it was struck. He realized that if the reaction was contained and channeled, it could be used to ignite powder charges and he eventually used his knowledge to create what was called a “pill lock” ignition system. His was the first step along the way to today’s modern primers and the path wound through England and America for more than a hundred years.