Bullet
This article is about firearms projectiles. For other uses, see Bullet (disambiguation).







A bullet is a kinetic projectile, a component of firearm ammunition that is shot
from a gun barrel. They are made of a variety of materials, such as copper, 
lead, steel, polymer, rubber and even wax; and are made in various shapes and 
constructions (depending on the intended applications), including specialized 
functions such as hunting, target shooting, training, and combat. Bullets are 
often tapered, making them more aerodynamic. Bullet size is expressed by weight
and diameter (referred to as "caliber") in both imperial and metric measurement
systems.[1] Bullets do not normally contain explosives[2] but strike or damage 
the intended target by transferring kinetic energy upon impact and penetration.

	
	

7.5×55mm Swiss full metal jacket, armor piercing, and tracer, spitzer 
projectiles. The three bullets on the right show cannelure evolution Duration: 
5 seconds.0:05 Schlieren image sequence of a bullet traveling in free-flight,
demonstrating the air pressure dynamics surrounding the bullet




Description






The term bullet is from Early French, originating as the diminutive of the word
boulle (boullet), which means "small ball".[3] Bullets are available singly (as
in muzzle-loading and cap and ball firearms)[4] but are more often packaged with
propellant as a cartridge ("round" of ammunition) consisting of the bullet
(i.e., the projectile),[5] the case (which holds everything together), the
propellant (which provides the majority of the energy to launch the projectile),
and the primer (which ignites the propellant). Cartridges, in turn, may be held
in a magazine or a belt (for rapid-fire automatic firearms). Although the word
bullet is often used in colloquial language to refer to a cartridge round, a
bullet is not a cartridge but rather a component of one.[6] This use of the term
bullet (when intending to describe a cartridge) often leads to confusion when a
cartridge and all its components are specifically being referenced.

	


The sound of gunfire (i.e. the "muzzle report") is often accompanied with a loud
bullwhip-like crack as the supersonic bullet pierces through the air, creating
a sonic boom. Bullet speeds at various stages of flight depend on intrinsic
factors such as sectional density, aerodynamic profile and ballistic coefficient
, as well as extrinsic factors such as barometric pressure, humidity, air 
temperature and wind speed.[7][8] Subsonic cartridges fire bullets slower than
the speed of sound, so there are no sonic booms. This means that a subsonic
cartridge, such as .45 ACP, can be substantially quieter than a supersonic
cartridge, such as the .223 Remington, even without the use of a suppressor.[9]

Bullets shot by firearms can be used for target practice or to injure or kill 
animals or people. Death can be by blood loss or damage to vital organs, or even
asphyxiation if blood enters the lungs. Bullets are not the only projectiles 
shot from firearm-like equipment: BBs are shot from BB guns, airsoft pellets are
shot by airsoft guns, paintballs are shot by paintball markers, and small rocks
can be hurtled from slingshots. There are also flare guns, potato guns (and spud
guns), tasers, bean bag rounds, grenade launchers, flash bangs, tear gas, RPGs,
and missile launchers.



Speed 
Bullets used in many cartridges are fired at muzzle velocities faster than the 
speed of sound[10][11]—about 343 metres per second (1,130 ft/s) in dry air at 
20 °C (68 °F)—and thus can travel substantial distances to their targets before
any nearby observers hear the sound of the shots.

Rifle bullets, such as that of a Remington 223, leave the muzzle at speeds of up
to 4,390 kilometres per hour (2,730 mph). A bullet from a 9 mm Luger handgun, 
reaches speeds of only 2,200 kilometres per hour (1,370 mph).  Similarly, an 
AK-47, has a muzzle velocity of about 2,580 kilometres per hour (1,600 mph).[12]



History






The first true gun evolved in China from the fire lance (a bamboo tube that
fired porcelain shrapnel) with the invention of the metal hand cannon sometime
around 1288, which the Yuan dynasty used to win a decisive victory against 
Mongolian rebels. The artillery cannon appeared in 1326 and the European hand 
cannon in 1364. Early projectiles were made of stone.  Eventually it was 
discovered that stone would not penetrate stone fortifications, which led to the
use of denser materials as projectiles.  Hand cannon projectiles developed in a 
similar manner. The first recorded instance of a metal ball from a hand cannon
penetrating armor was in 1425.[13] Shot retrieved from the wreck of the Mary 
Rose (sunk in 1545, raised in 1982) are of different sizes, and some are stone
while others are cast iron.[14]

	
	

	Round shot from the 16th century Mary Rose English warship, showing both
	stone and iron ball shot


The development of the hand culverin and matchlock arquebus brought about the 
use of cast lead balls as projectiles. The original round musket ball was 
smaller than the bore of the barrel. At first it was loaded into the barrel just
resting upon the powder. Later, some sort of material was used as a wadding 
between the ball and the powder as well as over the ball to keep it in place,
[15] it held the bullet firmly in the barrel and against the powder. (Bullets 
not firmly set on the powder risked exploding the barrel, with the condition 
known as a "short start".)[16]

The loading of muskets was therefore easy with the old smooth-bore Brown Bess
and similar military muskets. The original muzzle-loading rifle, however, was
loaded with a piece of leather or cloth wrapped around the ball, to allow the
ball to engage the grooves in the barrel. Loading was a bit more difficult, 
particularly when the bore of the barrel was fouled from previous firings. For 
this reason, and because rifles were not often fitted for bayonets, early rifles
were rarely used for military purposes, compared to muskets.







There was a distinct change in the shape and function of the bullet during the 
first half of the 19th century, although experiments with various types of 
elongated projectiles had been made in Britain, America and France from the 
first half of the 18th century onwards.[17][18] In 1816, Capt. George 
Reichenbach of the Bavarian army invented a rifled-wall musket using
cylindro-conical ammunition.[19] In 1826, Henri-Gustave Delvigne, a French
infantry officer, invented a breech with abrupt shoulders on which a spherical
bullet was rammed down until it caught the rifling grooves.  Delvigne's method,
however, deformed the bullet and was inaccurate. In 1855, a detachment of 1st 
U.S. Dragoons, while on patrol, traded lead for gold bullets with Pima Indians
along the California–Arizona border.[20][21]

Square bullets have origins that almost pre-date civilization and were used in 
slings. They were typically made out of copper or lead. The most notable use of
square bullet designs was by James Puckle and Kyle Tunis who patented them, 
where they were briefly used in one version of the Puckle gun. The early use of 
these in the black-powder era was soon discontinued because of the irregular and
unpredictable flight patterns.

	
	

Matchlock musket balls, alleged to have been discovered on the battlefield
of Naseby (1645)




Pointed bullets






Delvigne continued to develop bullet design and by 1830 had started to develop 
cylindro-conical bullets. His bullet designs were improved by Francois Tamisier
with the addition of "ball grooves" which are known as "cannelures", which moved
the resistance of air behind the center of gravity of the bullet.[22] Tamisier
also developed progressive rifling: the rifle grooves were deeper toward the 
breech, becoming shallower as they progressed toward the muzzle. This causes the
bullet to be progressively molded into the grooves which increases range and 
accuracy.[23][24] 

	
Delvigne further developed cylindro-spherical (left) and cylindro-conical
bullets (middle), which received the bullet grooves developed by Tamisier
for stability








Among the first pointed or "conical" bullets were those designed by Captain John
Norton of the British Army in 1832. Norton's bullet had a hollow base made of
lotus pith that on firing expanded under pressure to engage with a barrel's
rifling.[25] The British Board of Ordnance rejected it because spherical bullets
had been in use for the previous 300 years.[26] Renowned English gunsmith 
William Greener invented the Greener bullet in 1836. Greener fitted the hollow
base of an oval bullet with a wooden plug that more reliably forced the base of
the bullet to expand and catch the rifling. Tests proved that Greener's bullet
was effective, but the military rejected it because, being two parts, they
judged it as too complicated to produce.[27]

	
Before Tamisier's invention, the orientation of a cylindro-conical bullet tended
to remain along its inertial axis, progressively setting it against its 
trajectory and increasingly meeting air resistance, which rendered the bullet's
movement erratic.


The carabine à tige, developed by Louis-Étienne de Thouvenin in 1844, was an
improvement of Delvigne's design. The rifle barrel has a forcing plug in the
breech of the barrel to mold the bullet into the rifling with the use of a
special ramrod. While successful in increasing accuracy, it was difficult to
clean. 







The soft lead Minié ball was first introduced in 1847 by Claude-Étienne Minié, 
a captain in the French Army. It was another improvement of the work done by 
Delvigne. The bullet was conical in shape with a hollow cavity in the rear, 
which was fitted with a small iron cap instead of a wooden plug.  When fired, 
the iron cap forced itself into the hollow cavity at the rear of the bullet, 
thus expanding the sides of the bullet to grip and engage the rifling. In 1851,
the British adopted the Minié ball for their 702-inch Pattern 1851 Minié rifle.
In 1855, James Burton, a machinist at the U.S.  Armory at Harper's Ferry, West 
Virginia, improved the Minié ball further by eliminating the metal cup in the 
bottom of the bullet.[28][29] The Minié ball first saw widespread use in the 
Crimean War (1853-1856). Roughly 90% of the battlefield casualties in the 
American Civil War (1861-1865) were caused by Minié balls fired from rifled 
muskets.[30] A similar bullet called the Nessler ball was also developed for 
smoothbore muskets.[31]

	
	

	Minié ball ammunition
	

	
	

	1855 Minié ball design from the U.S. Arsenal, Harper's Ferry, West Virginia


Between 1854 and 1857, Sir Joseph Whitworth conducted a long series of rifle
experiments and proved, among other points, the advantages of a smaller bore
and, in particular, of an elongated bullet. The Whitworth bullet was made to fit
the grooves of the rifle mechanically. The Whitworth rifle was never adopted by
the government, although it was used extensively for match purposes and target 
practice between 1857 and 1866. In 1861, W. B. Chace approached President 
Abraham Lincoln with an improved ball design for muskets. In firing over the 
Potomac River, where the Chace ball and the round ball were alternated, Lincoln
observed that the Chace design carried a third or more farther fired at the same
elevation. Although Lincoln recommended testing, it never took place.[32]

Around 1862, W. E. Metford carried out an exhaustive series of experiments on
bullets and rifling, and he invented the important system of light rifling with
increasing spiral and a hardened bullet. The combined result was that, in 
December 1888, the Lee–Metford small-bore (.303", 7.70 mm) rifle, Mark I, was
adopted for the British army. The Lee–Metford was the predecessor of the 
Lee–Enfield.[33]



Modern bullets






The next important change in the history of the rifle bullet occurred in 1882, when Lieutenant Colonel Eduard Rubin, director of the Swiss Army Laboratory at Thun, invented the copper-jacketed bullet — an elongated bullet with a lead core in a copper jacket. It was also small bore (7.5 and 8 mm) and it is the precursor of the 8 mm Lebel bullet adopted for the smokeless powder ammunition of the Lebel Model 1886 rifle. The surface of lead bullets fired at high velocity may melt from the hot gases behind and friction within the bore. Because copper has a higher melting point, and greater specific heat capacity, and higher hardness, copper-jacketed bullets allow greater muzzle velocities.

European advances in aerodynamics led to the pointed spitzer bullet. By the beginning of the 20th century, most world armies had begun the transition to spitzer bullets. These bullets flew for greater distances more accurately and transferred more kinetic energy. Spitzer bullets combined with machine guns greatly increased lethality on the battlefield.

	
	.270 Winchester ammunition:

100-grain (6.5 g) – hollow point
115-grain (7.5 g) – FMJBT
130-grain (8.4 g) – soft point
150-grain (9.7 g) – round nose
	








Spitzer bullets were streamlined at the base with the boat tail. In the 
trajectory of a bullet, as air passes over a bullet at high speed, a vacuum
is
created at the end of the bullet, slowing the projectile. The streamlined
boat
tail design reduces this form drag by allowing the air to flow along the
surface of the tapering end. The resulting aerodynamic advantage is
currently
seen as the optimum shape for rifle technology. The first combination
spitzer
and boat-tail bullet, named balle D by its inventor Captain Georges
Desaleux,
was introduced as standard military ammunition in 1901, for the French
Lebel
Model 1886 rifle.

	
	

	.303 inch (7.7 mm) centrefire, FMJ rimmed ammunition


A ballistic tip bullet is a hollow-point rifle bullet that has a plastic tip on
the end of the bullet. This improves external ballistics by streamlining the
bullet, allowing it to cut through the air more easily, and improves terminal
ballistics by allowing the bullet to act as a jacketed hollow point. As a side
effect, it also feeds better in weapons that have trouble feeding rounds that
are not full metal jacket rounds.



Design
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Bullet designs have to solve two primary problems. In the barrel, they must
first form a seal with the gun's bore. If a strong seal is not achieved, gas
from the propellant charge leaks past the bullet, thus reducing efficiency and 
possibly accuracy. The bullet must also engage the rifling without damaging or 
excessively fouling the gun's bore and without distorting the bullet, which will
also reduce accuracy. Bullets must have a surface that forms this seal without 
excessive friction. These interactions between bullet and bore are termed 
internal ballistics. Bullets must be produced to a high standard, as surface
imperfections can affect firing accuracy.

	
	

	A bullet in mid flight


The physics affecting the bullet once it leaves the barrel is termed external 
ballistics. The primary factors affecting the aerodynamics of a bullet in flight
are the bullet's shape and the rotation imparted by the rifling of the gun 
barrel. Rotational forces stabilize the bullet gyroscopically as well as 
aerodynamically. Any asymmetry in the bullet is largely canceled as it spins. 
However, a spin rate greater than the optimum value adds more trouble than good,
by magnifying the smaller asymmetries or sometimes resulting in the bullet 
breaking apart in flight. With smooth-bore firearms, a spherical shape is 
optimal because no matter how the bullet is oriented, its aerodynamics are 
similar. These unstable bullets tumble erratically and provide only moderate
accuracy; however, the aerodynamic shape changed little for centuries. 
Generally, bullet shapes are a compromise between aerodynamics, interior 
ballistic necessities, and terminal ballistics requirements.

Terminal ballistics and stopping power are aspects of bullet design that affect
what happens when a bullet impacts with an object. The outcome of the impact is
determined by the composition and density of the target material, the angle of
incidence, and the velocity and physical characteristics of the bullet. Bullets
are generally designed to penetrate, deform, or break apart.  For a given 
material and bullet, the strike velocity is the primary factor that determines
which outcome is achieved.

Bullet shapes are many and varied. With a mold, bullets can be made at home for
reloading ammunition, where local laws allow. Hand-casting, however, is only 
time- and cost-effective for solid lead bullets. Cast and jacketed bullets are
also commercially available from numerous manufacturers for handloading and are
most often more convenient than casting bullets from bulk or scrap lead.



Propulsion
Propulsion of the ball can happen via several methods:

by using only gunpowder (as in flintlock weapons)
by using a percussion cap and gunpowder (as in percussion weapons)
by using a cartridge



Materials






Bullets for black powder, or muzzle-loading firearms, were classically
molded from pure lead. This worked well for low-speed bullets, fired at
velocities of less than 450 m/s (1,475 ft/s). For slightly higher-speed
bullets fired in modern firearms, a harder alloy of lead and tin or
typesetter's lead (used to mold linotype) works very well. For even higher
-speed bullet use, jacketed lead bullets are used. The common element in all
of these, lead, is widely used because it is very dense, thereby providing a
high amount of mass—and thus, kinetic energy—for a given volume. Lead is
also cheap, easy to obtain, easy to work, and melts at a low temperature,
which results in comparatively easy fabrication of bullets.

	
	

Expanding bullet loaded in a 6.5×55mm before and after expanding. The long base
and small expanded diameter show that this is a bullet designed for deep 
penetration on large game. The bullet in the photo traveled more than halfway 
through a moose before coming to rest, performing as designed.



Lead: simple cast, extruded, swaged, or otherwise fabricated lead slugs are
the simplest form of bullets. At speeds of greater than 300 m/s (1,000 ft/s)
(common in most handguns), lead is deposited in rifled bores at an 
ever-increasing rate. Alloying the lead with a small percentage of tin and/or
antimony serves to reduce this effect but grows less effective as velocities are
increased. A cup made of harder metal, such as copper, placed at the base of the
bullet and called a gas check, is often used to decrease lead deposits by 
protecting the rear of the bullet against melting when fired at higher 
pressures, but this does not solve the problem at higher velocities.  A modern
solution is to powder coat the lead projectile, encasing it in a protective 
skin, allowing higher velocities to be achieved without lead deposits.
Jacketed lead: bullets intended for even higher-velocity applications
generally have a lead core that is jacketed or plated with gilding metal,
cupronickel, copper alloys, or steel; a thin layer of harder metal protects
the softer lead core when the bullet is passing through the barrel and
during flight, which allows delivering the bullet intact to the target.
There, the heavy lead core delivers its kinetic energy to the target. Full
metal jacket or "ball" bullets (cartridges with ball bullets, which despite the
name are not spherical, are called ball ammunition) are completely encased
in the harder metal jacket, except for the base. Some bullet jackets do not
extend to the front of the bullet, to aid expansion and increase lethality;
these are called soft point (if the exposed lead tip is solid) or hollow
point bullets (if a cavity or hole is present). Steel bullets are often
plated with copper or other metals for corrosion resistance during long
periods of storage. Synthetic jacket materials such as nylon and Teflon have
been used, with limited success, especially in rifles; however, hollow point
bullets with plastic aerodynamic tips have been very successful at both
improving accuracy and enhancing expansion. Newer plastic coatings for
handgun bullets, such as Teflon-coated bullets, are making their way into
the market.

Hard cast solid bullet (left), with gas check (center) and lubrication (right)






Solid or monolithic solid: mono-metal bullets intended for deep penetration
in big game animals and slender shaped very-low-drag projectiles for long
range shooting are produced out of metals like oxygen-free copper and alloys
like cupronickel, tellurium copper and brass (e.g., highly machinable UNS
C36000 free-cutting brass). Often these projectiles are turned on precision
CNC lathes. In the case of solids, and the ruggedness of the game animals on
which they are used, e.g., the African buffalo or elephant, expansion is
almost entirely relinquished for the necessary penetration. In shotgunning,
"slug" loads are often solid large single lead projectiles, sometimes with a
hollow point, used for deer or wild pig hunting in jurisdictions that do not
allow hunting with rifles (because a missed slug shot will travel
considerably less far than a rifle bullet).






	

Fluted: in appearance, these are solid bullets with scalloped sides
(missing material). The theory is that the flutes produce hydraulic jetting
when passing through tissue, creating a wound channel larger than that made
by conventional expanding ammunition such as hollow point bullets.
Hard cast: a hard lead alloy intended to reduce fouling of rifling grooves
(especially of the polygonal rifling used in some popular pistols). Benefits
include simpler manufacture than jacketed bullets and good performance
against hard targets; limitations are an inability to mushroom and
subsequent over-penetration of soft targets.
	
Blank: wax, paper, plastic, and other materials are used to simulate live
gunfire and are intended only to hold the powder in a blank cartridge and to
produce noise, flame and smoke. The "bullet" may be captured in a 
purpose-designed device or it may be allowed to expend what little energy it 
has in the air. Some blank cartridges are crimped or closed at the end and do 
not contain any bullet; some are fully loaded cartridges (without bullets) 
designed to propel rifle grenades. The force of the expanding gas from blank 
cartridges can be lethal at short range; numerous tragic accidents have occurred
with blank cartridges (e.g., the death of actor Jon-Erik Hexum).  Practice: made
from lightweight materials like rubber, wax, wood, plastic, or lightweight 
metal, practice bullets are intended for short-range target work only. Because
of their weight and low velocity, they have limited range.

	
	

A modern centerfire cartridge consisting of the following: 1. bullet, as the
projectile; 2. metallic case, which holds all parts together; 3. propellant,
for example gunpowder or cordite;4. rim, which provides the extractor on the
firearm a place to grip the case to remove it from the chamber once fired;
5. primer, which ignites the propellant.

Polymer: these are metal-polymer composites, generally lighter and having
higher velocities than pure metal bullets of the same dimensions. They
permit unusual designs that are difficult with conventional casting or
lathing.
Less lethal, or less than lethal: Rubber bullets, plastic bullets, and
beanbags are designed to be non-lethal, e.g., for use in riot control. They
are generally low velocity and are fired from shotguns, grenade launchers,
paint ball guns, or specially designed firearms and air gun devices.
Incendiary: these bullets are made with explosive or flammable mixtures in
the tips that are designed to ignite on contact with a target. The intent is
to ignite fuel or munitions in the target area, thereby adding to the
destructive power of the bullet.
Exploding: similar to the incendiary bullet, this type of projectile is
designed to explode upon hitting a hard surface, preferably the bone of the
intended target. Not to be mistaken for cannon shells or grenades with fuse
devices, these bullets have only cavities filled with a small amount of high
explosive depending on the velocity and deformation upon impact to detonate.
Exploding bullets have been used in various heavy machine guns and in anti
-materiel rifles.
Tracer: these have hollow backs, filled with a flare material. Usually this
is a mixture of magnesium, a perchlorate, and strontium salts to yield a bright
red color, although other materials providing other colors have also sometimes 
been used. Tracer material burns out after a certain amount of time. This allows
the shooter to visually trace the flight path of the projectile and thus make 
necessary ballistic corrections, without having to confirm projectile impacts 
and without even using the sights of the weapon.  This type of round is also 
used by all branches of the United States military in combat environments as a
signaling device to friendly forces.  Normally it is loaded at a four to one 
ratio with ball ammunition.
Armor-piercing: jacketed designs where the core material is a very hard,
high-density metal such as tungsten, tungsten carbide, depleted uranium, or
steel. A pointed tip is often used, but a flat tip on the penetrator portion
is generally more effective.[34]
Nontoxic shot: steel, bismuth, tungsten, and other alloys prevent release
of toxic lead into the environment. Regulations in several countries mandate
the use of nontoxic projectiles especially when waterfowl hunting. It has
been found that birds swallow small lead shot for their gizzards to grind
food (as they would swallow pebbles of similar size), and the effects of
lead poisoning by grinding of lead pellets against food means lead poisoning
effects are magnified. Such concerns apply primarily to shotguns firing
pellets (shot) and not bullets, but there is evidence suggesting that
consumption of spent rifle and pistol ammunition is also hazardous to
wildlife.[35] Reduction of hazardous substances legislation has also been
applied to bullets on occasion to reduce the impact of lead on the
environment at shooting ranges.
Blended-metal: bullets made using cores from powdered metals other than
lead with binder or sometimes sintered.
Frangible: designed to disintegrate into tiny particles upon impact to
minimize their penetration for reasons of range safety, to limit
environmental impact, or to limit the shoot-through danger behind the
intended target. An example is the Glaser Safety Slug, usually a pistol
caliber bullet made from an amalgam of lead shot and a hard (and thus
frangible) plastic binder designed to penetrate a human target and release
its component shot pellets without exiting the target.
Multiple projectile: bullets that are made of separate slugs that fit
together inside the cartridge and act as a single projectile inside the
barrel as they are fired. The projectiles part in flight but are held in
formation by tethers that keep the individual parts of the "bullet" from flying 
too far away from each other. The intention of such ammo is to increase hit
chance by giving a shot-like spread to rifled slug firing guns, while
maintaining a consistency in shot groupings. Multiple impact bullets may be
less stable in flight than conventional solid bullets because of the added
drag from the tether line holding the pieces in formation, and each
projectile affects the flight of all the others. This may limit the benefit
provided by the spread of each bullet at longer ranges.




Treaties and prohibitions
Poisonous bullets were a subject to an international agreement as early as the 
Strasbourg Agreement (1675). The Saint Petersburg Declaration of 1868 prohibited
the use of explosive projectiles weighing less than 400 grams.[36] The Hague 
Conventions prohibits certain kinds of ammunition for use in war. These include
poisoned[37][38] and expanding[39][40] bullets.  Protocol III of the 1983 
Convention on Certain Conventional Weapons, an annexed protocol to the Geneva 
Conventions, prohibits the use of incendiary ammunitions against civilians.[41]



Types of bullets
Some types of bullets include:



Armor piercing (sometimes with a depleted uranium or other heavy metal core)
Armor-piercing fin stabilized discarding sabot round
Cast
Expanding (hollow point, soft point)
Frangible
Full metal jacket (also known as "ball" ammunition)
Hollow-base
Hollow-point
Hydra-Shok


Nosler partition
Plastic-tipped
Sabot
Saboted light armor penetrator
Spitzer
Semiwadcutter
Total metal jacket
Very low drag
Wadcutter
Wax




See also 

Flechette
List of handgun cartridges
List of rifle cartridges
Meplat
Smart bullet
Table of handgun and rifle cartridges
The Second Amendment to the US Constitution