Gunpowder was invented by the Chinese in the 9th century. Three centuries later it was first used to propel a projectile. The gun was born.
Gunpowder, also known as Black Powder, is a mixture of charcoal, sulpher, and saltpeter. Saltpeter is Potassium Nitrate. whose chemical formula is KNO3. It is the nitrate, NO3, that is the critical component of gunpowder.
When heated, nitrates decompose into Nitrogen and Oxygen. This reaction releases energy, but more importantly, makes oxygen available to burn the charcoal and sulpher. When confined, as in a gun barrel, gunpowder burns very rapidly creating a large volume of gas at high pressure.
The first guns were just tubes, capped at one end. Gunpowder was poured in the open end, then a projectile (often a ball of metal) was dropped in on top of the gunpowder. The ball had to fit well to get the maximum advantage from the burning gunpowder.
The powder was ignited through a small hole, the touch-hole, at the closed end of the tube. The rapidly expanding gasses created by the burning powder forced the ball down the tube and out the open end.
Although the details have changed, the principals of how guns work are still the same. Nine hundred years later, high-pressure gasses, created by burning solid propellants, are still pushing bullets down gun barrels.
The first improvement to guns was to attach the tube, or barrel, to some sort of handle to make the gun easier to hold. The handle became known as the stock.
Next came a better method of lighting the powder. A priming pan was
added under the touch-hole. A small amount of powder placed in the
priming pan was ignited by a smouldering cord called a match.
The match was dipped into the priming pan by one end of a lever, called the serpentine, when the other end was toggled by the shooters finger. More complex systems of levers were also used.
When flint-on-steel ignition replaced the matchlock it became necessary to have the flint strike the steel with some force. The flint is held in a spring-loaded hammer. The hammer is held by a sear. The sear is released by the trigger.
Until the 1800s guns worked by lighting the powder in the priming pan in one way or another. Matchlocks gave way to wheel-locks and then to flintlocks. Early in the 1800s experiments began with fulminates; inherently unstable chemical compounds that detonate when subjected to mechanical stress.
In 1822 fulminate of mercury was placed in a small metal cup. The cup was placed
over the end of a hollow nipple which protruded from the touch-hole in
place of the priming pan. When the trigger was pulled, the hammer would
fall on the percussion cap, causing the fulminate to detonate and light
the main powder charge. By 1839 Flintlocks were obsolete.
Percussion-ignition has some key advantages over earlier ignition types.
Pouring powder and ramming balls down the barrel of a gun was slow and potentially dangerous. In 1845 French inventor, Louis Nicolas Flobert created the first metallic cartridge by placing a small lead ball in a percussion cap. This was a significant development. All the expendables needed to fire a gun were now self-contained.
The .22 Short was developed in 1857 for Smith and Wesson's new revolver. This was a rimfire, meaning that the priming compound was in the rim of the cartridge. Later, a percussion cap was placed in the center of the base of the cartridge case. This arrangement is known as centerfire.
The components that make up a centerfire cartridge are the primer, the cartridge case, the powder, and the bullet.
Metallic cartridges allow breech loading; loading from the back end of the barrel, as opposed to muzzle loading; loading from the front end of the barrel.
Breech loading is faster, safer, makes it easy to use rifled barrels, and paves the way for repeaters.
The disadvantages are the extra component, namely the cartridge case, and the additional complexity required to insert the cartridge and extract the fired case.
Metallic cartridges, whether rimfire or centerfire, rely on a firing pin to provide the mechanical energy to detonate the primer. The firing pin can be part of the hammer, struck by the hammer, or not involve a hammer at all. In this last case the firing pin is driven directly by the main spring and is called a striker.
Rifling is spiral grooves cut into the inside of the barrel. The purpose of the rifling is to put spin on the bullet. Spin stabilizes the bullet in flight, makes it more accurate, and increases its range.
Rifling first appeared in guns in the late 1500s but did not become common until the 1700s.
Barrels that are not rifled are referred to as smooth-bore.
Guns that must be reloaded after each shot are called single shot.
Early multi-shot concepts included multiple barrels, multiple loads in the same barrel fired from front to back with a moving lock, and early revolvers, including the very successful Colt cap and ball designs. Although multiple shots could be fired all these guns were still slow to load.
Smith and Wesson introduced their Model 1 seven shot revolver in 1857. This "tip up" revolver (the barrel hinged out of the way allowing the cylinder to be removed for reloading) fired the new .22 Short rimfire.
The Spencer lever action repeater firing the 56-56 Spencer rimfire cartridge entered production in 1860.
Also in 1860 B. Tyler Henry produced the .44 Henry rimfire cartridge and a lever action rifle to fire it.
These were the first repeating arms to take advantage of breech loading metallic cartridges.
Repeaters need a supply of ammunition to cycle through the action. This ammunition is stored in the magazine.
Muzzle loaded firearms are fairly simple. Their only moving parts are the hammer and trigger. With the advent of breech loaders and then repeaters, firearms got more complex.
The mechanical scheme of a gun is referred to as its action. There are many types of actions. There are single action revolvers and double action revolvers. There are lever actions and pump actions. No doubt there are actions yet to be invented.