The caplock mechanism or "percussion" lock was the successor of the flintlock mechanism

Flintlock mechanism

The flintlock mechanism was a firing mechanism used on muskets and rifles in the 17th, 18th, and 19th centuries. It is commonly referred to as a "flintlock" , though that term is also commonly used for the weapons themselves as a whole, and not just the lock mechanism.The flintlock was developed in...

 in firearm

Firearm

A firearm is a weapon that launches one, or many, projectile at high velocity through confined burning of a propellant. This subsonic burning process is technically known as deflagration, as opposed to supersonic combustion known as a detonation. In older firearms, the propellant was typically...

 technology, and used a percussion cap

Percussion cap

The percussion cap, introduced around 1830, was the crucial invention that enabled muzzleloading firearms to fire reliably in any weather.Before this development, firearms used flintlock ignition systems which produced flint-on-steel sparks to ignite a pan of priming powder and thereby fire the...

 struck by the hammer to set off the main charge, rather than using a piece of flint to strike a steel frizzen

Frizzen

The frizzen, historically called the steel, is an "L" shaped piece of steel hinged at the rear used in flintlock firearms. It is positioned over the flash pan so as to enclose a small priming charge of black powder next to the flash hole that is drilled through the barrel into where the main...

.

The rudimentary percussion system was developed by Rev. Alexander John Forsyth

Alexander John Forsyth

Alexander John Forsyth was a Scottish Presbyterian clergyman who invented the percussion ignition.Gunsmiths like Joseph Manton invented more reliable forms of ignition, like the tube lock in 1814...

 as a solution to the problem that sitting birds would startle when smoke puffed from the powder pan of his flintlock shotgun, giving them sufficient warning to escape the shot. His invention of a fulminate-primed firing mechanism deprived the birds of their early warning system, both by avoiding the initial puff of smoke from the flintlock powder pan, as well as shortening the interval between the trigger pull and the shot leaving the muzzle. Forsyth patented his ignition system in 1807. However, it was not until after Forsyth's patents expired that the conventional percussion cap system was developed.

The caplock offered many improvements over the flintlock. The caplock was easier to load, more resistant to weather, and was much more reliable than the flintlock. Many older flintlock weapons were later converted into caplocks so that they could take advantage of this increased reliability.
The caplock mechanism consists of a hammer, similar to the hammer used in a flintlock, and a nipple (sometimes referred to as a "cone"), which holds a small percussion cap. The nipple contains a tube which goes into the barrel. The percussion cap contains a chemical compound called mercuric fulminate

Mercury(II) fulminate

Mercury fulminate, or Hg2, is a primary explosive. It is highly sensitive to friction and shock. It is mainly used as a trigger for other explosives in percussion caps and blasting caps...

 or fulminate of mercury, whose chemical formula is Hg(ONC). It is made from mercury, nitric acid

Nitric acid

Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...

and alcohol. When the trigger releases the hammer, it strikes the cap, causing the mercuric fulminate to explode. The flames from this explosion travel down the tube in the nipple and enter the barrel, where they ignite the main powder charge.

External links

• How percussion caps work