Sunday, June 10, 2012

The Chemistry of a Bullet




A gunman pulls the trigger and a bullet flies out the barrel in a split second. So the question is, how? What goes on in that very short period of time when the cartridge is hit to when the bullet leaves the barrel? To understand this we have to get down to the basics.

 In order for the shot to exit the barrel there must be a force exerted, this force is seen in Newton’s second low of motion, “When a body is acted upon by a constant force, the resulting acceleration is inversely proportional to the mass of the body and is directly proportional to the applied force.” The force that is used to expel the shot from the barrel is achieved through the use of gunpowder. Gunpowder is the propellant used and at a homogeneous mixture of “KNO3 at 74.0%, sulfur at 10.4%, and charcoal at 15.6%,” it is very flammable (23, Rinker). But this is just a portion of the material used, because in order for the gunpowder to light a primer must be used. 
When the firing pin of the rifle hits the center of the case compressor (the extended bump at the back of the cartridge), it will ignite the primer which will then ignite the powder when the “flame passes through vents in the anvil”(19, Rinker). Primers used today consist mainly of “lead styphnate” and, depending on the manufacturer, a mixture of some of the following; “TNT, lead or copper sulphocyanide, lead peroxide, sulfur, tetryl, barium peroxide, and barium nitrate” (19, Rinker). The gunpowder, as a propellant, has “chemical energy” which is converted to move the projectile down the barrel. 
    This conversion involves three steps; chemically the propellant “converts or decomposes almost completely into a gas.” Thermodynamically the energy is “changed into heat which in turn creates motion-power,” and physically the “hot gas pushes the projectile, [then] it reacts to the friction and creates a [sic] recoil” that will force the rifle up and back against the shooter(21, Rinker). Once this process has occurred, it will cause a buildup of a great amount of pressure behind the bullet due to the expansion of the gases. This gas will propel the bullet down the rifled interior of the barrel, which give the bullet spin, and out into the air.

Rinker, Robert. Understanding Firearm Ballistics. Fourth ed. U.S.A.: Mulberry House Publishing,1996. Print.



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