A primer is a small, disposable copper or brass cup, 1..2mm in diameter. In the cup is a precise, dried droplet 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 explosive 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.
Noncorrosive primers are somewhat less reliable when stored for many years, but far easier on gun. Most civilian ammunition uses noncorrosive primers.
The percussion cap replaced the posder 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 which 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 exploded by concussion.
This invention was gradually developed, and 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 by a perforated nipple, and by
replacing the cock or hammer which held the flint by a smaller
hammer with a hollow to fit on 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, shot guns and pistols.
Caps are used in cartridgess, grenades, and RPGss.History