How Guns Work: The Percussion Cap

Have you ever wondered what made the modern gun possible? It was not the gun; it was the ignition. Modern firearms, as we know them, started with the percussion cap.

In a previous article I described how flintlock firearms worked. The flint and steel method made gun ownership and military standard issue weapons a reality and shaped world we have inherited, but now I am going to cover the system that stole its crown and lead to the firearms we have today. The caplock, aka percussion system, featured in movies such as Glory and Jeremiah Johnson is alive, and surprisingly hearty, today thanks to many replica and custom guns that still use the system. Many shooters who are new to muzzleloading purchase caplocks, and I was no exception. My previous article on the Colt 1851 is a prime example of my deep roots in caplock guns—as are numerous firearms I have bought or built. But whatever was wrong with the good old flintlock that needed altering in the first place?

Problems with the Flintlock

Just because flintlock guns were the best you could have for over two hundred years does not mean it was a perfect mechanism. The most vital problems were:

1. Flints had to be sharp, otherwise they will not shave metal off the frizzen and create the shower of sparks needed for ignition.
2. The flint’s frizzen must be dry to catch sparks. The lock must be waterproofed to work in adverse conditions.

Improving the Technology

Inventors experimented with chemicals that exploded when struck, but were too volatile to use, that is, until 1812 when someone (there are many arguments over who that “someone” was, precisely) had the brilliant idea to contain the percussion-sensitive explosive in a small, water resistant copper cap to contain the flame of ignition. By the 1820s, old flintlock guns were converted to use the new system and new guns were being churned out to take advantage of the technological improvement.

The explosive cap also made possible the first practical repeating arms, like the early revolvers. It also made the cartridge possible. Packing the explosive into the rim of a case gave us the first rimfires, such as the .22 Short of 1857. Later centerfire cartridges featured a cap in the middle of the case for ignition (used in most popular ammo shot today). Even with cartridges on the scene, caplock guns were the most commonly used in the American Civil War (1861-65). Before the war was over, caplocks were obsolete, but the technology it made thrived.

How It Works

Caplocks are very simple weapons to operate, so it comes as no surprise that the first weapons in a muzzleloading enthusiast’s arsenal are often caplock guns. Here is how the percussion system works.

Normally, there is a threaded tube that fits into the barrel’s firing chamber horizontally. It is hollow within, but closed off to the outside (revolvers don’t need a tube). A hollow nipple is threaded vertically into the tube and is the avenue of ignition. Once the gun is loaded from the breech or muzzle, the shooter pulls back the hammer and pushes a cap onto the nipple. After that, all that’s left is for the shooter to cock the hammer and fire. When the cap pops from the hammer fall, it sends flame through the nipple and tube and into the powder charge, sending the projectile forward through the barrel.

Final Thoughts

Caplock technology, and the guns that utilized it, may not have lasted very long, but, as we’ve seen, they were a great step toward developing the modern firearms produced today. Before the cap, a waterproof firearm was nearly impossible to produce, but a gun that could fire repeatedly without reloading was only a dream. The caplock ultimately solved that conundrum and made the cartridge possible. The pinnacle of ammunition, as we know it, started in 1812. The next time you hit the range, enjoy the little piece of history that fires every time you pull the trigger. Sounds like a great excuse to go shooting to me.