Little Copper Cap: How a Pinch of Mercury Cap Remade the Infantry
The entire cap revolution is housed in a copper cup about four millimeters high. A pinch of primer is placed at the bottom, and varnish or a circle of foil is placed on top. It is placed on the nipple with a finger, broken by the hammer, and ignites the main charge. Two hundred years later, the same thing, only recessed into the base of a brass cartridge case, still lives in every AK cartridge. Meanwhile, the road to this cap was a long one, and it began with a Scottish pastor who was tired of the flintlock.
The Pastor Who Was Tired of Flint
By the early 19th century, the flintlock seemed like a solved problem. A trigger holding a flint struck a steel fire starter (frizzen, a hinged steel plate above the pan), sparks rained down onto an open pan containing priming powder, from where the fire traveled through the touchhole into the barrel. A design honed by two centuries of refinement, it had exactly two problems, both fundamental.
The first was dampness. The priming powder on the open pan drew moisture from the air, and in rain or fog, the lock simply refused to fire. The second was the delay and flash. On the best muskets, the time from trigger pull to bullet flight was about 40–50 milliseconds; on production muskets, it was longer. All this time, an open flame burned on the pan right next to the shooter's face, clearly visible to any game.
Scottish Presbyterian pastor Alexander Forsyth
Scottish Presbyterian pastor Alexander Forsyth was an avid hunter and in his own writings complained directly about both shortcomings: the "delay between the strike of the flint and the shot" and the "flash that warns the game." He was familiar with the work of Edward Howard, who in 1800 had produced mercury fulminate, a compound that detonates on impact. He realized that if the flash on the shelf were replaced by a shock on the compound, the system would gain two advantages.
An example of a Forsyth roller lock mounted on a pistol grip to demonstrate its operating principle. The roller has a number indicating it was manufactured in 1808, but the square end of the lock plate indicates it was assembled around 1810–1811.
Forsyth took out a patent on April 29, 1807. The design was nicknamed scent-bottle lock — "a bottle-lock": a rotating magazine with a dispenser, shaped like a perfume bottle, measured out a dose of the initiating compound, which the trigger struck. It worked convincingly. However, the magazine, holding about two dozen shots of mercury fulminate, hanging on the side of the breech, was suitable for a gentleman in the swamp, but not for a soldier running with a fixed bayonet. It was complicated, dangerous, and, most importantly, expensive. The Forsyth lock was not adopted by the mass army. But its chemicals, packaged differently, were.
Capsule: a focus on simplicity
And then it begins story, whose priority is still being debated, and here we must go into a little more detail. The idea of a disposable cap occurred to several people simultaneously between 1814 and 1822.
Anglo-American Joshua Shaw later claimed to have assembled a working copper cap in Philadelphia in 1816, but he only filed a patent in 1822. London gunsmith Joseph Manton patented related designs for pipe cap locks as early as 1816. London gunsmith Joseph Egg further developed the design and is considered one of the main popularizers of the copper cap in England. Parisian industrialist François Prélat took out a French patent in 1818. Modern historians weapons They say cautiously: the invention was hanging in the air, and it will no longer be possible to determine who exactly put the final point.
Joseph Manton's percussion cap lock, patented in 1816. The corrosive properties of mercury fulminate, combined with the critical location of the firing pin, prevented this design from being successful, but it was the first serious violation of Forsyth's patent. The lock required a flat bullet with a diameter of 0,110 inches. The detached hammer reveals the critical firing pin.
But we can accurately describe what they came up with. The primer is a stamped copper (later brass) cup about four millimeters high and about five in diameter. This is precisely the famous size #11, still used in muzzleloading sports. At the bottom is a thin layer of percussion-initiating compound, covered with a drop of varnish or a circle of foil to protect against friction and moisture. The mass of the compound is tens of milligrams, not grams or "half a gram," as is sometimes written.
The choice of copper is no accident. The metal is malleable: it can be stamped on a simple press by the thousands per hour. It's soft: it deforms under the hammer's strike just enough to transmit the shock to the contents, preventing hard fragments from flying into the shooter's face. It doesn't rust: the cup can be carried in a pocket for months. It's inexpensive: copper was a common material in Europe by the 1820s.
And most importantly: the cap is disposable. No magazine, no dispenser, no rotating mechanisms. You fire a shot, scrape off the rest with your fingernail, put on a fresh one, and cock the hammer. The operation is shorter than loading a flintlock pan with priming powder from a horn. It was this simplicity that decided the outcome, with chemistry and ballistics playing second fiddle. And it was this simplicity, not chemistry, that paved the way for the percussion cap to become part of military ammunition: more on that later.
Mercury fulminate and why it was scary to make
Inside the cup is the substance that was the whole point of the whole thing: mercury fulminate (Hg(CNO)2), the mercury salt of fulminate acid. It's produced by reacting mercury with nitric acid and ethanol; the process was described by Howard in 1800 and remained essentially unchanged throughout the 19th century. It's a grayish-white powder, and a pinch is enough to ignite the main charge in the barrel.
Its main property is detonation by mechanical impact. Mercury fulminate explodes from impact, friction, and sometimes its own weight in a large container. This is what distinguishes a percussion cap lock from a flintlock as a class: the fire is generated directly from the material compressed by the impact; a spark is not required. The closed channel of the nipple, isolated from air, can be dipped in water, and the cap will still detonate: the dry mixture inside the cup remains dry.
Pure mercury fulminate, however, is not used: it explodes too violently, corrodes copper, and ruins the barrel with decomposition products. The actual composition in the 19th century was a mixture: mercury fulminate as an initiator, potassium chlorate as an oxidizer, antimony sulfide (Sb₂S₃) or sulfur as a combustible additive, and sometimes ground glass to increase shock sensitivity. In other words, the composition consisted not of a single substance, but of four or five, and each manufacturer kept the balance between them secret and adjusted experimentally. (Incidentally, according to a version well-known among gunsmiths, the recipe of the English Eley Brothers factory from the early 1830s was long considered lost; it was restored in the 20th century using archival purchasing records.)
Production was a dangerous occupation. Mercury fulminate was synthesized in batches of several kilograms at cap factories in the 1830s and 1840s, dried in a thin layer, and dosed into cups by hand or using simple machines. Explosions occurred regularly at cap factories in England and France. Dosing and loading operations were carried out primarily by women and teenagers (they had smaller fingers and cheaper labor) in workshops without modern ventilation, working for twelve hours a day next to open containers. Chronic mercury poisoning—tremors, tooth loss, neurological disorders—was recorded by factory doctors, but it was rarely included in production statistics: those who left due to illness were replaced, and that was the end of the record. Mercury fulminate remained in primers until the early 20th century, when it was gradually replaced by lead azide and lead styphnate, which were less insidious to manufacture and less corrosive to the barrel. The principle of percussion initiation, however, remained the same. It remains to be seen how this principle was incorporated into weapons.
A rod instead of a shelf
For the cap to work, the weapon required minimal modification. The open pan containing the priming powder disappeared; in its place, a hollow steel rod was screwed into the breech— nipple, also known as a firearm tube or priming rod. A narrow channel ran through it, connecting the outer end to the powder chamber. A primer was placed on the end. A hammer, converted from a flint-and-jaw design into a simple hammer with a flat or cup-shaped striker, struck it from above.
What happened at the engineering level is worth discussing separately. The open system with a scattering of gunpowder on a shelf has been transformed into a closed one: a ready-made portion of the initiating composition is packaged in a sealed container, and the fire path from the composition to the main charge passes through a short, closed channel. Moisture from the outside no longer affects this device.
The timing of the action is a bit more complicated. According to measurements taken by German engineer Wolfgang Kick in the late 19th century, and later comparative tests on surviving examples and replicas, the best flintlocks were approximately 40–50 milliseconds from the descent to the departure of the bullet, the cap in 25–35The difference is one and a half times, sometimes two times. These figures weren't obtained from a single standardized test, but rather in different years on different installations, so they should be treated as orders of magnitude rather than exact parameters. But they're fair orders of magnitude.
(The “6000-shot test” of two Brown Bess pistols circulating on the internet, with the impressive result of “six misfires against a thousand,” adds little to this picture: the original source is lost in the retelling.)
The most important thing, however, was the conversion. Tens of thousands of flintlock muskets were converted to caplocks in regimental and arsenal workshops in the 1830s and 1840s with a simple operation: remove the pan, solder and tin the hole, drill a new one for the nipple, and replace the trigger. Old barrel, old stock, new lock. The army didn't need to buy new weapons; it converted the ones it had. The caplock revolution took place without a budget scandal—a rare occurrence in the history of military technology.
The painting "Defend Sevastopol!" by Vasily Nesterenko depicts one of the key moments of the defense—the repulse of the Anglo-French-Turkish assault on Malakhov Kurgan in June 1855.
From nipple to sleeve
The percussion cap lock was first tested in combat in the middle of the century. The Crimean War of 1853–1856 was the first major European campaign where both sides fought en masse with percussion cap weapons. The French Model 1842 infantry rifle, the British Model 1853 Enfield rifle, and Russian conversions—all used a nipple and cap. The American Civil War of 1861–1865 finally cemented the result: with the Minié bullet and percussion cap, it became the most widely used infantry weapon of the conflict, firing millions of shots in the swamps of Virginia and the winters of Tennessee.
At this point, the primer had already begun to move from the weapon's surface into the cartridge, and here the French engineering school took the lead. As early as 1808–1812, the Parisian gunsmith of Swiss descent, Jean Samuel Pauli, in partnership with the same Prélat, assembled the first prototype of a unitary cartridge with a primer in the base. The design was crude and never went into production, but the idea remained.
Prussian gunsmith Johann Nikolaus von Dreyse took a different approach. His Model 1841 rifle featured a bolt-action mechanism and a paper cartridge with a percussion cap at the base of the bullet; a long bolt needle pierced the paper and gunpowder to strike the cartridge from behind. The solution worked (the Prussians used it to defeat the Austrians at Sadovaya in 1866), but it was a dead end: the needles broke from constant contact with hot combustion gases, gases escaped through the bolt joint, and cleaning became a ritual.
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The Battle of Königgrätz (also known as the Battle of Sadovaya), July 3, 1866, by Carl Röchling.
The Battle of Königgrätz (also known as the Battle of Sadovaya), July 3, 1866, by Carl Röchling.
The problem wasn't the needle itself, but the fact that Dreyse's primer was located inside the powder charge, and the needle passed through the fire with each shot. The solution was obvious: relocate the primer in the base of the cartridge, striking it from behind without penetrating the powder. This is what Chasspot did. His Model 1866 rifle: the primer is in the base, the needle strikes it through a short channel from the outside, and a rubber obturator on the bolt prevents gas leakage. There was still paper in the cartridge case, but the design was already modern.
At the same time, another French line of development was working in civilian firearms. In 1845, Louis-Nicolas Flaubert developed the .22 BB Cap, essentially a large cap with a sealed bullet, without a separate propellant charge. Initially, it was a cartridge for parlor and parquet shooting, for indoor shooting ranges with a range of 10 meters, a popular pastime for the wealthy at the time. But it was from this cartridge that the rimfire cartridge evolved, where the primer is pressed into the rim of the cartridge case. Two decades later, Flaubert's compatriot Clément Potte, followed by the Englishman Edward Boxer and the American Hiram Berdan, perfected the center-fire cap: a small cup containing the same primer, recessed into a socket on the base of a brass cartridge case.
Flaubert cartridges
Seven names over half a century—Pauli, Dreyse, Chasspot, Flaubert, Potte, Boxer, Berdan—represent the speed at which the primer traveled inside the cartridge. With the advent of the centerfire, it ceased to be a separate component carried by a soldier in a box and became what it remains to this day: the smallest and most important part of the cartridge. The brass circle, approximately five millimeters in diameter, at the base of a modern 5,45×39 or 7,62×54R cartridge case is a direct descendant of the copper cap of the 1820s. The composition inside is different: lead styphnate with additives, which has become almost universal since the 1930s. The principle is the same: striker strike, deformation, detonation, and a flame beam into the main charge.
Over the past two hundred years, almost everything about the primer has changed. Black powder gave way to smokeless powder, the lead bullet acquired a jacket, the rimmed cartridge case became rimless, manual loading was replaced by automatic loading systems, the musket evolved into the assault rifle and machine gun. The primer itself has remained the same: the composition has changed, the metal of the primer cup has changed, but the design has not. Two hundred years in service without any major alterations. A biography that fits entirely on a thumbnail.
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