10 Innovations That Led to the Modern Bullet

In the ancient world, the metaphor for a brilliant idea just might have been a firecracker exploding over someone's head. That's because firecrackers contained black powder, the invention of 10th-century Chinese pyromaniacs. It didn't take long before some bellicose warrior or jealous husband discovered he could launch a projectile using the same mixture of saltpeter (potassium nitrate), sulfur and charcoal.

The earliest black-powder weapons belonged to the Arabs -- bamboo tubes reinforced with metal that used a charge of black powder to shoot arrows. These were replaced by bronze hand cannons, which required two men to fire. One held the weapon while a second inserted a glowing coal or wire into a hole drilled in the solid end, or breech. This ignited the black powder, which sent a round ball -- the first bullet -- roaring from the open end of the cannon.

Over time, weapons became far more sophisticated, but they still relied on the same ancient chemical process, what scientists describe today as deflagration. In this type of reaction, a spark ignites a small mass of black powder, which doesn't explode but combusts rapidly to create a large amount of expanding gases held back by a non-fixed plug. That plug, of course, is the bullet, which fits tightly enough in the barrel that gases can't escape around it. As the gases expand and encounter the resistance, they propel the bullet out of the muzzle.

It would be another nine centuries before something better came along.

Most people think of the arms race as a competition occurring between the U.S. and the former Soviet Union during the Cold War. However, the struggle of nations to exert superiority over their enemies by amassing more and better weapons has been an ongoing reality for eons. The lowly bullet is no exception. The earliest ammunition consisted of small round stones, but these had little effect on armor-covered warriors. This led arms manufacturers to explore metal bullets, made by pouring molten metal into a mold and letting it harden.

Iron balls were popular for a while, but they were difficult to make, required extreme temperatures to melt and often ruptured the musket barrels trying to fire them. Then, in the early 1600s, lead balls started flying over battlefields. Lead had a low melting point, so it could be cast in a ladle over a wood fire. Soldiers and hunters could resupply their ammunition while they cooked dinner. And because they were softer, lead balls posed little risk of damaging gun barrels. These bullets, also known as musket balls or "rounds," would reign supreme until the 1800s and the development of an aerodynamic projectile.

Early smoothbore muskets received lead balls through the muzzle. The balls were smaller than the diameter of the bore, so that, upon firing, they bounced along the barrel until they exited. That bouncing didn't do much for accuracy. Then, in the 15th century, German gunmakers invented rifling – the process of cutting spiral grooves into the inside wall of the barrel. These grooves dug into the projectile as it moved down the barrel, causing it to spin and giving it a truer flight. Rifling worked better if the projectile fit snugly in the barrel, which meant lead balls needed a cover, or patch, to increase their diameter.

A major breakthrough arrived in the 1850s, courtesy of a French army officer named Claude-Étienne Minié. His eponymous bullet was still made of lead, but it was conical, not round. When hot gases from black powder combustion expanded into the hollow-based Minié ball, they caused the soft bullet to flare out and grip the rifled barrel. This meant that the innovative bullets could be made smaller than the bore without diminishing the spin they acquired. And they didn't require a patch, which made them easier to load.

The Minié ball -- the first cylindroconoidal bullet -- improved the accuracy of shooters tremendously. During the Civil War, which saw the first widespread use of these bullets, Union and Confederate infantrymen hit their targets more often and at far greater distances.

Like The Boss belted out in "Dancing in the Dark": "You can't start a fire, you can't start a fire without a spark." Although Springsteen was referring to romance, the same idea applies to bullets. For a weapon to work, there must be a spark or ember to ignite the primer, which in turn ignites the black powder. Flintlock pistols and rifles accomplished this by striking a piece of flint against a serrated piece of steel. Sparks from the flint striking the steel fell into the pan containing primer. The primer burned in a rapid flash, thereby lighting the powder charge.

Flintlock weapons worked well, but they had a disadvantage: the delay between the cock falling and the gun firing. A few inventors wondered if fulminating salts, which exploded on impact, might be a better alternative. Unfortunately, the salts were very sensitive to shock, friction and sparks, making them too unstable to be practical. Then, in 1800, the English chemist Edward Howard managed to isolate mercury fulminate, a relatively stable version of the compound. When the Rev. Alexander Forsyth mixed mercury fulminate with potassium chlorate, he produced a very reliable and safe priming agent. By the 1820s, this new primer was the key ingredient in the percussion cap, a small copper "top hat" that sat on an anvil or nipple. When the hammer struck the cap, it ignited the mercury fulminate, causing a flame to enter the barrel and initiate combustion of the powder charge.

The invention of black powder may have been one of humankind's most significant achievements, but it led to a messy battlefield. In a protracted fight, during which soldiers discharged their weapons many times, a thick veil of smoke filled the air, sometimes rendering the enemy invisible. By the 1800s, chemists and inventors were hunting for a better propellant.

The answer came from the plant kingdom, in the form of cellulose. This macromolecule, or long chain of repeating glucose units, is common in plant cells and can be obtained from wood pulp or the short fibers of cotton. In 1846, the Swiss chemist Christian Friedrich Schönbein took cotton and dipped it in a mixture of nitric and sulfuric acids, causing the hydroxyl groups of the cellulose to be replaced by nitro groups. The result was an extremely flammable substance known as nitrocellulose or guncotton. Unfortunately, it tended to decompose spontaneously and explode without warning. Then, in the 1880s, French engineer Paul Vieille found that when nitrocellulose was mixed with certain stabilizers, it became much less volatile. This led directly to a new type of gunpowder, commonly known as smokeless powder, that revolutionized ammunition. Now a soldier could fire his weapon and not disappear behind a plume of white smoke.

The modern form of smokeless powder -- cordite -- contains nitrocellulose, nitroglycerine and petroleum jelly. In its final form, it looks like small, graphite-colored grains.

Before the 19th century, primer, powder and bullet existed as independent components. To shoot a musket, for example, someone had to pour a little powder into the firing pan, pour some more powder down the barrel and then ram a ball against the charge. Touching an external spark to the primer initiated the firing sequence. Paper cartridges made this a bit easier by providing the shooter a premeasured packet of powder, although he still needed to tear open the paper and dispense powder into both pan and barrel.

All of this changed in the late 1800s with the introduction of the bullet cartridge -- a self-contained unit that housed primer, propellant and projectile in a brass casing. Parisian gunmaker Louis Flobert had already produced cartridges in 1840, but they were small and reserved primarily for indoor target practice. Daniel Wesson (of Smith & Wesson fame) saw Flobert's experiment and, in the 1850s, invented the first brass cartridge ready for the battlefield and the backwoods. Wesson's design packed a small bit of mercury fulminate in the rim of the brass case. Black powder filled the hollow tube of the case, and a bullet sat on top.

The entire unit could be placed into the breech of the gun, eliminating the need for patches, percussion caps or other separate components. The cartridge itself formed the seal at the breech. When the weapon's hammer struck the rim of the cartridge, it ignited the primer, which then spread the flame through the black powder, forcing the bullet down the barrel.

As revolutionary as rim-fire cartridges were, they had some disadvantages. The biggest was the cartridge itself, which needed a thinner shell to ensure that it would deform when the hammer struck it. But the thinner casing limited the explosive force it could contain. As a result, rim-fire cartridges held less powder and generated less firepower.

To overcome these limitations, gun manufacturers quickly evolved the cartridge so it could incorporate a percussion cap, filled with shock-sensitive primer, within a unified, thicker-walled structure. The cap sat in the middle of the shell's base, which is how it came to be called a center-fire cartridge. Gunmakers also had to modify their weapons to fire the new cartridge, including either a firing pin or a striker. In the former, a spring-loaded hammer transferred its energy to a blunt-nosed rod, which struck the percussion cap. In the latter, the hammer struck the percussion cap directly. In either case, applying a sharp blow to the cap ignited the primer, which then ignited the powder and fired the bullet.

Because center-fire cartridges generate more power, they can fire larger bullets, which makes them the most common type of ammunition used in firearms today.

The introduction of smokeless powder presented challenges to weapons manufacturers. Because nitrocellulose-based propellants produced higher temperatures and pressures than black powder, they moved bullets down the barrel with greater velocity. As they made the journey, softer lead bullets couldn't stand up to the increased friction. Their outer layers were stripped off and left in the barrel, causing fouling.

The solution, of course, was to give bullets a thicker skin, or a jacket. Gunmakers chose copper or alloys of copper and zinc to cover their pistol bullets. They used a harder jacket of steel or cupronickel for rifle and machine-gun bullets. In both cases, the core of the bullet still contained lead, except in armor-piercing bullets, which used inner cores of hardened steel.

In military weapons, bullets possess a full-metal jacket (FMJ), meaning the jacket covers the entire projectile. These bullets are sometimes called non-expanding because they retain their shape as they pass through a target. For soldiers and military surgeons, this is a good thing, for FMJ bullets do less damage to internal tissues and organs. Big-game hunters have far different requirements. They need a bullet that will cause massive internal trauma so their prey will go down quickly. They use expanding bullets, which mushroom out as soon as they encounter resistance. The jacket of such a bullet only extends over a portion of the lead projectile, leaving the tip exposed. When a soft-point bullet strikes a target, such as a deer or a bear, the tip expands and flares out, allowing it to inflict more damage on internal organs.

When a bullet exits a rifle barrel, it can be traveling between 800 and 1,000 meters per second (2,625 to 3,280 feet per second) -- much too fast to be seen with the naked eye. In the days of black powder, a fired bullet sometimes left a trail of smoke, marking the path of the projectile through the air. But with the advent of smokeless powder, shooters received no feedback about a bullet's trajectory until it arrived at the target.

Enter the tracer round, which includes an additional incendiary compound, usually a phosphorus or magnesium mixture, in the base of the bullet. When a tracer is fired, the powder in the cartridge both propels the bullet and lights the incendiary mixture. As the bullet travels through the air, it gives off an intense light and trails smoke, helping the shooter see the bullet go downrange. Military forces often use this type of ammunition in machine guns, in which every fifth round in the magazine or belt includes a tracer.

Today, tracers can produce a variety of colors for daytime and nighttime applications. White tracers can be seen during the day, while red and green ones can be seen at night.

Not much happened to bullets in the hundred years following the introduction of metal cartridges containing copper-clad projectiles. They worked amazingly well and, as a result, changed little over time. Then, in the late 20th century, law enforcement agencies began to form modern hostage rescue units tasked with apprehending criminals and terrorists in the midst of civilian personnel. Often, such interactions occurred in extremely close quarters, where bullets could pass through a target and then strike an innocent bystander. Meanwhile, law enforcement agencies were also seeing a number of situations in which officers were injured or killed by bullets, fired at close range, ricocheting off solid objects.

This led to a search for a new kind of bullet, one that would still possess stopping power but would break apart when it struck a wall or other solid surface. Eventually, ammunition makers devised a way to take small particles of composite material that they either pressed or glued together. Once formed into a bullet shape, the so-called frangible -- or soft round -- doesn't receive a copper jacket. That way, if the bullet strikes a hard object, the composite material simply breaks into small, grain-sized particles. If it strikes a bad guy, like a terrorist trying to hijack a plane, it enters the body and then breaks apart, causing a significant wound without the risk of over-penetration.