From Wikipedia, the free encyclopedia.
The percussion cap or primer was the crucial invention needed to make fire-arms that could fire in any weather. Before this development, firearms used igniters with flints or matches to set fire to a pan of gunpowder.
A primer is a small, disposable copper or brass cup, 1 to 2mm in diameter. In the cup is a precise amount of stable, but shock-senstive explosive, such as lead azide or potassium perchlorate.
A striker hits the outside of the cup, which bends, and the explosive is crushed on an anvil. The shock-sensitive chemical compound explodes, igniting a secondary charge of gunpowder or other explosive.
Caps were originally manually placed on nipples on the outside of single-shot muzzle-loading weapons. Pulling the trigger released a hammer to crush the cap against the nipple.
Eventually, caps were incorporated into the rear of metallic cartridges. A small stamped anvil was added to the design, placed inside the cup to make the modern replaceable primer.
Corrosive primers use stable, long-lived explosives that generate acidic residues in a gun. They are popular with the military because they work reliably under severe conditions.
Noncorrosive primers are somewhat less reliable when stored for many years, but far easier on guns. Most civilian ammunition uses noncorrosive primers.
The percussion cap replaced the powder pan of the wheel lock and flint-lock rifles. It was only generally
applied to the British military musket (the Brown Bess) in
1842, a quarter of a century after the invention of percussion
powder and after an elaborate government test at Woolwich in
1834.
The invention that made the percussion cap possible
was patented by the Rev. A. J. Forsyth in 1807, and consisted
of priming with a fulminating powder made of chlorate of
potash, sulphur, and charcoal, which was exploded by concussion.
This invention was gradually improved, and came to be used, first in a
steel cap, and then in a copper cap, by various gunmakers and
private individuals before coming into general military use
nearly thirty years later.
The alteration of the military
flint-lock to the percussion musket was easily accomplished
by replacing the powder pan with a perforated nipple, and by
replacing the cock or hammer which held the flint by a smaller
hammer formed with a hollow made to fit around the nipple when released by the
trigger. On the nipple was placed the copper cap containing
the detonating composition, now made of three parts of chlorate
of potash, two of fulminate of mercury and one of powdered
glass.
The detonating cap, thus invented and adopted, brought
about the invention of the modern cartridge case, and rendered
possible the general adoption of the breech-loading principle
for all varieties of rifles, shotguns and pistols.
Caps are used in cartridgess, grenades, and Rocket propelled grenades.History
