Evolution of Guns
Gunpowder was first discovered in 9th century China and is still currently the most important discovery for modern day warfare. It has undergone many changes in both it's it's chemical composition and method of use of the centuries. This page looks at the History of these changes and the Physics behind a gun and the mechanics which is specific to gunpowder weapons.
Information in these green boxes is considered advanced reading! Read this information if you want to learn more.
The History of Gunpowder
HISTORY OF GUNPOWDER
Gunpowder was first discovered in 9th century China by alchemists and originally consisted of Sulphur, charcoal and Potassium Nitrate. When ground together they formed a powder which was refered to as "Serpentine". When mixing the powder they often mixed it with a liquid such as water to reduce the danger of any potential sparks setting it off.
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The first ancestor to the modern day firearm was the fire lance. This weapon was used in China during the late 11th century and the 12th century. IT consisted of a spear or halberd with a tube attached to the end containing gunpowder inside and a projectile of some sort, from darts to metal balls. The range of these weapons was very short a limited to only a few feet and therefore they were mostly used in hand-to-hand combat to give the wielder an advantage over their adversary.
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The first evidence of a more traditional firearm being used was a cave sculpture in Sichuan depicting a man holding a vase shaped hand cannon with flames and a cannonball being fired out of it.
The first sruviving example of a firearm is a bronze hand cannon which dates back to 1288 and was discovered in Manchuria.
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Knowledge of gunpowder slowly spread west, either because of the Silk Road, through trade between East Asian civilisations and Arabs, or due to Mongolian conquest into the Islamic. In 1260, it is written that firearms were used by a Mamluk army against the Mongol horde at Ain Jalut, which is situated in present day Israel. The Mamluk army proved successful and defeated the Mongol army. This was the first time a Mongol army had been defeated in battle in 43 years since they launched their westward thrust from Mongolia. This demonstrates the success which gunpowder weapons can have.
In 1322, Christian forces lay siege to the city of Algeciras, which is a port locate on the South coast of the Iberian Peninsula. It was currently in the possession of the Islamic Moors. In the besieging army were 5 English earls. In defence of the city, the Moors used cannons which caused vast damage to the Christian encampments and siege equipment, and were referred to as "thunder" due to the sound they made. It is highly likely that the English earls, having seen the effectiveness of these weapons, brought the ideas back home after the siege. This was one of the first times that gunpowder had been used in combat in Europe.
The first ever bit of writting about a metal cannon was in a manuscript which was given to Edward III when he first came into power in 1327. It was a vase shaped device and fired arrows at high power towards the enemy.​
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During the 100 years’ war cannons became more and more advanced. A very important battle which showed their effectiveness on the battlefield was the Battle of Creçy in 1346. The English army was trying to retreat to the North coast of France, having captured Caen, the capital of Normandy. Meanwhile a French army was gathering around Paris ready to push back the invaders. The English were unable to cross the Somme river due to the bridges being destroyed, which enabled the French army to catch up with them. The English army had approximately 4000 men-at-arms, 5000 spearmen, 7000 archers and 5 cannons. The French army on the other hand had up to 80,000 men, including about 6000 crossbowmen which were positioned in front of the main army. The English, holding a position at the top of the hill, let loose on their bows and cannons while still out of range of the crossbows and massacred the crossbowmen. In panic, the crossbowmen retreated back through the French knights, who were trying to charge up the hill at the same time, all while there was a storm of arrows and cannonballs all around them. The battle was a decisive victory for the English, by the end of the battle, the British casualties were minimal, yet the French had lost almost half their army, including two kings, a duke, 10 counts and 3 archbishops.
A map showing the battle formations during the Battle of Creçy
Devlopment of Handheld Firearms
DEVELOPMENT OF HANDHELD WEAPONS
A musket
The 14th century saw in introduction of more portable handheld firearms, such as the Culverin or hand bombard. These weapons were still not as effective as the English longbow, but did not require the same extensive training. They consisted of a smooth, long barrel with a handle and a small hole at the base through which they could light the gunpowder. The next few hundred years saw vast improvements in hand cannons, moving onto arquebusiers in the 15th century. These were a light general purpose firearm designed for infantry. During its life cycle it it witnessed earliest forms of mechanically firing of a firearm, the first being the matchlock.
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In a matchlock musket, there is a slow burning match clamped to an S-shaped arm. When the trigger is pulled the arm was lowered so that the match came into contact with the priming powder in a pan attached to the side of the barrel. When lit, the sparks entered the barrel through a small hole in its base.
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After the matchlock came the wheellock, in the 16th century. This method had a similar idea, of lighting the priming powder in the pan, but the way in which it is lit is different. Now, attached to the S-shaped arm was a flint. When the trigger was pulled this came into contact with a spinning roughened metallic wheel. The contact of the flint and the spinning metal was enough to generate a spark.
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In the 17th century, flintlocks came into use. These weapons solved a problem which had been plaguing muskets for centuries. Previously the pan which stored the priming powder was covered by a lid, and this had to be removed manually. In a flintlock musket, the lid has a piece of steel sticking up from it, called a frizzen. When the trigger is pulled, a flint attached to the hammer strikes the frizzen which flakes of particles of the steel. The friction generated by the force of the blow is enough to ignite these particles which cause sparks. When the hammer strikes the frizzen it is knocked back and lifts the lid off the pan, revealing the gunpowder and allowing it to be ignited and to fire the gun. This mechanism was dominant for almost 200 years, and remained completely unchanged. The most famous flintlock musket was Brown Bess which was used by the British army during the era of the British Empire.
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In the early 19th century, caplocks became prominent. These have a hammer, just like the flintlock, but with a percussion cap instead of a pan with primer in it. A percussion cap is a small cartridge containing Mercury fulminate (Hg(ONC)2) as it is highly sensitive to friction and pressure. The hammer would strike the cartridge which would ignite and in turn ignite the powder in the barrel. The main benefit of this was that it was not prone to misfires in damp weather, unlike the flintlock muskets.
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While the the firing method was developing, the technique of rifling was also being developed. Rifling is the method of making grooves on the inside of the barrel to give the bullet a spin around the axis of its direction of travel, which adds stability and accuracy to the bullet. Adding a spin to a projectile had been known for a long time, as arrows often had their fletchings curved to create the spin, and rifling was developed early on in firearms’ life cycle in the early 16th century, but wasn’t common until the 19th century. There are several reasons why it wasn’t used for several centuries, even though the benefits of it were common knowledge.
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The gunpowder used at the time, called black powder nowadays, when combusted, left behind a vast amount of solid waste. There was a study conducted which showed that, by mass, 55.91% of the products of the combustion of black powder were solid, 42.98% were gasses which provides the pressure to fire the gun. In a smoothbore musket this is fine as the musket ball doesn’t need to be a tight fit in the barrel. For a gun with rifling the bullet needs to be a tight fit, so as more and more solid material built up in the grooves and on the inside of the barrel it became harder and harder to load often preventing the rifle for being used. This problem was even worse because when the black powder was first loaded into the gun, it would leave particles along the sides of the barrel which made the barrel fouling occur much faster.
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The black powder produced a lot of smoke which would obscure the battlefield, causing the longer ranged and accurate rifles almost useless, and the faster fire rate of the smoothbore muskets was much preferred.
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Rifles were expensive to produce in the large quantities required to equip an entire army. They also took much longer to make than muskets.
The early use of rifles in the American Revolution proved pivotal in the American victory in the late 18th century. Many of the American militia were using Kentucky Long Rifles, which were based on German hunting rifles, the designs for which had been brought to America by German immigrants. The British on the other hand were still using their smoothbore Brown Bess, which were accurate up to 50m. The Kentucky rifles were accurate to well over 200m, and the men who used these acted as snipers, picking off British officers and cannoneers.
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The development of cartridges and breech loaders enabled rifles to be much more effective on the battlefield. The cartridges contained the black powder, preventing loose powder from fouling the barrel and the breech loaders meant that bullets didn’t need to be loaded down the muzzle, to the breach so there was no longer an issue with the gun becoming too difficult to load.
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In the late 19th century there was a new type of gunpowder was developed, called smokeless powder. It was called smokeless due to the lack of solid residue left after combustion. It also produced a much greater force per volume than black powder. This new powder enabled the development of automatic weapons, as there was now much less residue so the guns were more reliable and didn’t jam so easily
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The discovery of Mercury fulminate enabled the invention of the cartridge, a fully enclosed package, originally by paper, but then also brass, containing primer, gunpowder and the bullet, and these came into common use in the middle of the 19th century and caused breech loaded rifles (where the cartridge was placed directly in the base of the barrel, rather than being inserted down the muzzle) to become the dominant firearm. These weapons were detonated by a pin putting pressure on the primer while in the sealed brass, which ignites the primer causing a chain reaction to the gunpowder. This is still the method we use today for firing and loading rifles.
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The view down a rifled barrel
The physics of guns - or at least the flight of the bullet is broken down into two separate sections:
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Internal Ballistics: the Physics of the bullet whilst in the barrel
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External Ballistics: the Physics of the projectile through a fluid such as air
PHYSICS OF THE GUN
Let’s consider a bullet of mass mb in front of some gunpowder of mass mp in a barrel with a cross sectional area A. Let’s assume that the bullet completely fills the barrel, so any gases produced by the powder are unable to get around it, in which case we can model our gun as an expanding piston, and let’s also assume that the process happens so quickly that there is negligible heat transfer to the bullet and the surrounding barrel, in other words our system can be modelled adiabatically.
In adiabatic expansion of gas, PV is constant throughout, where P and V are the pressure and volume of the gas in the barrel propelling the bullet and γ is the ratio of the specific heat capacities at constant pressure and at constant volume of the gas produced by the powder.
The equation for pressure relative to energy density is given as:
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where E is energy, and initial volume of the powder is:
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where ρp is the density of the powder. Therefore the total length of the barrel which the case takes up immediately after combustion, assuming that the gunpowder all combusts into a gas immediately and that the gunpowder completely compact and fills all available space behind the bullet, is:
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The pressure acting upon the bullet as a function of length of gas as the gas expands is given by:
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The equation for the transfer of energy to the bullet from the gas is then:
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This can be integrated to show that:
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Which simplifies down to:
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If we assume that at the end of the barrel the energy is split evenly between the super-heated gas and the bullet according to mass, and that all of the powder turned into gas then the energy of the bullet can be represented as such:
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Which therefore means that the velocity of the bullet leaving the barrel is given by:
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Internal Ballisitics
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External Ballistics
The torque of a precessing system is given by the following equation:
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where φ is the angle between the length of the bullet and the axis of precession, r is the distance from the base of the bullet (the base of the precession) to the bullet's centre of mass, m is the mass of the bullet, L is the angular momentum and t is time. The change of angle due to precession is:
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A diagram showing how a bullet precesses and the nutation of a bullet looking along the axis of precession.
These two equations can both be used to substitute into the equation for angular velocity of the precession like so:
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and therefore:
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where I is the moment of inertia of the bullet and ω is the angular velocity about it's axis of symmetry.
The main equations which govern the motion of the bullet in the air are the SUVAT equations which can are described on thrown objects page.
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The Coriolis deflection is an effect viewed on an object moving in a rotational frame of reference, such as a bullet either travelling North or South on the surface of the Earth. The object appears to curve away from the original path. Objects in the Northern hemisphere appear to curve to the right, and objects in the Southern hemisphere curve to the left. The reason for this is because of the spherical nature of the Earth. The Earth spins to the East with a constant angular velocity, but as some parts of the Earth are further away from the axis of rotation, they travel at a greater linear speed. The Equator is the far away from the axis of rotation and therefore objects there travel the fastest due to the spin of the Earth. The objects always swerve to the right in the northern hemisphere, and to the left in the Southern hemisphere.
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An object fired from the equator in a northerly direction, will maintain the higher eastward velocity, and therefore will be travelling east faster than the ground below, so will appear to curve towards the East. The opposite occurs for an object travelling south towards the equator, the linear velocity of the ground increases, and therefore it appears to have a slower easterly velocity, and therefore curves westwards.
The apparent acceleration by the Coriolis Effect is given by the equation:
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where a is acceleration, v is the velocity of the object and Ω is the angular velocity of the Earth.
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Rifling greatly assists the bullet in its accuracy by minimising the unpredictable movements which can occur when a bullet leaves a barrel. Before rifling, musket balls would bounce off the sides of the barrel on its way out and swerve off in a direction when it exited the muzzle. Rifling added a spin to the bullets around its axis of the direction of travel. This spin enables the bullets to travel in a more straight line due to gyroscopic precession.
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Gyroscopic precession is the ability for an object rotating at high speed to resist movement to forces trying to change the direction in which the axis of rotation. Any wobble caused by exiting the muzzle will be counteracted by the angular momentum. Instead of being forced off target, the bullet starts to precess, making circular movements with its tip.
