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Bullet-proof vest

A bullet-proof vest (also called body armor) is an article of protective clothing that works as a form of armour to minimize injury from being hit by a fired bullet. They are commonly worn by police forces and the military.

The above name is a misnomer since such protective vests are of little or no protective value against rifles regardless of the type, style, materials or caliber of the rifle ammo or even against handgun caliber ammo fired from a rifle. The exception is the common .22 caliber LR, which can usually be stopped by these vests even when fired from a rifle. These vests have proven to be fully protective against handgun ammo fired from handguns, again, regardless of type, style, materials or caliber of the handgun ammo.

Some types of vests may be augmented with metal (steel or titanium), ceramic or polyethelene plates that provide extra protection to vital areas. These "trauma plates" have proven effective against all handguns and some rifles, if the bullet actually hits the plate. These types of vests have become standard in military use, as advances in ballistic technology have rendered kevlar only vests ineffective - The CRISAT NATO standard for vests includes titanium backing. Some vests are also designed to protect against knife attacks as well.

A vest does not protect the wearer by deflecting a bullet. Instead, the individual layers of material catch the bullet and spread its momentum over a larger portion of the body, defoming the round and hopefully bringing it to a stop before it can penetrate into the body. While a vest can prevent a bullet from penetrating, the wearer can still be affected by the kinetic energy of the bullet, with results ranging from bruises to serious internal injuries.

The oldest bullet-proof fabric was made from silk. This was cabable of stopping some slow rounds from black powder guns. A more modern "flak jacket" was developed in World War II from nylon fabric but was only capable of stopping flak and shrapnel, not bullets. Modern bullet-proof vests made from Kevlar were tested by United States police forces in 1975. Since then several new fibers for bullet-proof fabric have been developed besides Kevlar, such as DSM's Dyneema, Akzo's Twaron, Toyobo's Zylon or Honeywell's GoldFlex. These newer fibres are advertised as being lighter, thinner and more resistant than Kevlar, and consequently much more expensive.

Many urban legends exist about bullet-proof vests, the most popular, convoluted and contradictory is the mythical "cop killer bullet" legend. This myth, originally invented by NBC TV news in a 1982 special, claims that an ordinary handgun is capable of penetrating these vests, thus killing a cop, if a certain type of ammo (specifically, teflon-coated rounds) were fired from the handgun. In fact, no such ammo exists and not one law enforcement officer has ever been killed by any type of handgun bullet fired from any handgun penetrating one of these vests (if the bullet actually struck the protective area of the vest). However modern, small caliber, military-only rounds can easily penetrate most bullet-proof vests, for example the MP7 fires a 4.6 mm bullet (.18") that can pass through a twenty layer kevlar vest with 1.5 mm of titantium backing at 150 m, other military rounds are believed to be equally effective even when handgun fired.

Both the Underwriters Laboratories and the United States National Institute of Justice have specific performance standards for bulletproof vests. UL rates vests on the following scale (UL Standard 752) against penetration and also blunt trauma protection (denting):

In terms of kevlar, a IIA vest has around sixteen layers and a IIIA vest around thirty layers. A IIA vest is tested up to a .40 S&W bullet and a IIIA vest up to a .44 Magnum or 9 mm submachine gun bullet. Vests rated to III can stop a 7.62 mm x 51 NATO bullet and the inserted plates are at least 13 mm of ceramic, an IV vest has 18 mm of ceramic.

In addition, there are vests available for police dogs which offer a measure of protection for the animals.

See also physics of firearms, ballistics.