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Forensic Ballistics

Forensic ballistics Analysis of bullet impacts to determine the type. Firearm and tool mark examinations involve analyzing firearm, ammunition, and tool mark evidence in order to establish whether a certain firearm or tool was used in the commission of a crime 6

Ballistic experiments have been with us since ancient times, when war machines were slinging rocks over the walls of fortified towns. As a science it began with the study of flight-paths when shooting at targets. One of the first to apply the science of ballistics to criminology was Eugene Francois Vidocq, the first head of the French Sûreté.

The modern ballistics expert is concerned with three areas: 1. Internal ballistics: what happens inside a weapon when it is fired. a. Firing pin makes a distinct mark on the cartridge. b. Explosive pressure causes the bullet to expand slightly to fill the spiral 'rifling' grooves cut in the bore. c. Then the bullet spins as it passes down the barrel, but it leaves tell-tale marks on the bullet that are unique to that particular firearm. * The presence of rust or spider silk indicates the gun has not been fired recently. * At close range, particles from a wound may lodge inside the barrel. 

2. External ballistics: what happens to the bullet and residues outside the gun, including the direction and velocity of the shot, as well as any deviation in the trajectory.

Terminal ballistics Studies changes in trajectory and speed caused by ricochet and penetration of objects, and layered deposits on parts of the bullet accumulated as it contacts these objects. Includes examination of wound shape and extent of tissue damage. If a bullet cannot be removed for examination, its caliber can be measured by CT scanning. 10

Forensic Ballistics: the scientific analysis or interpretation of all ballistic related evidence and phenomenon with the sole purpose of interpreting or establishing the true facts in a shooting related incident. Ballistic related evidence includes: firearms, bullets, and cartridge cases. However a listing of Ballistic related phenomenon is endless, including: bullet holes, bullet damage on various mediums; bullet trajectories, and gunshot wounds.

Ballistic fingerprinting, Method to find the gun used in a crime by matching the bullet's striations (or striae) with the rifled barrel through which it was fired, or by matching marks on the cartridge case to marks in the chamber and breech. Application of toolmark identification. 14

Ballistics Terms to Know: Ballistics: the study of bullets and firearms Barrel: the long, metal tube that guides a projectile out of a firearm

Breech: end of barrel attached to firing mechanism of a firearm where the cartridge is loaded and unloaded Bullet: the projectile that is sent flying when a firearm is shot

Caliber a measure of the inside diameter of a firearm barrel Cartridge a case that holds a bullet, primer powder, and gunpowder

Firearm a weapon capable of firing a projectile using a confined explosive as a propellant Fully automatic: a firearm with a clip fed mechanism that fires repeatedly as long as the trigger is pressed

Gunshot Residue: (GSR) the tiny particles expelled from a firearm when it is fired. A.K.A trace evidence

chemists have developed a reliable new test for detecting the presence of gun shot residue. Above is a residue particle -- roughly 1/20 the size of a period -- that has been magnified 200 times with a digital microscope

Lands and Grooves: ridges (lands) and depressions (grooves) found on the inside of a firearm’s barrel that are created when the firearm is manufactured. Muzzle the end of the barrel where the projectile exits a firearm

Pistol a hand-held firearm Revolver: a pistol with a revolving cylinder

Rifle a firearm that has a long barrel, a long gun Rifling the spiral pattern of lands and grooves in the barrel of a firearm

Differences Between Rifles, Shotguns, and Handguns

Rifle Scopes

Semiautomatic a pistol with a clip-fed mechanism that fires one shot per pull of the trigger; the empty cartridge ejects and the next cartridge advances automatically

Shell casing: the metal (usually brass) housing for the gunpowder of a firearm Trajectory: the path of flight of a projectile

Education and Training: Ballistics are a branch of criminalistics in forensic science. Education and Training: The minimum requirement is a bachelor's degree in chemistry, biology, physics, molecular biology, or a related science. In the future, a master’s degree may be required. Many colleges and universities offer degrees and courses in forensic science. In deciding whether to get a degree in chemistry or biology, or one in forensic science, study the courses offered. At least 24 semester hours of either chemistry or biology is required and math is a must. The title of the degree is not as important as the courses taken.

You need to be good in math and science, and have knowledge of firearms. It can be rewarding job, knowing that with your help, you can find out the type of gun that a bullet came from, that may have hurt or killed someone. That would be a relatively easy problem to solve, compared to trying to figure out the angle and velocity of a bullet to have to hit a target when trying to find out if a person standing at point A could have possibly hit something or someone standing at point B.

To keep up with the many advances in science, criminalists must take continuing education courses all during their career. By passing a difficult examination, they may become certified by the American Board of Criminalistics (www.criminalistics.com/ABC). Entire forensic laboratories may prove their competence by becoming accredited by organizations such as the American Society of Crime Laboratory Directors/Laboratory Accreditation Board (www.ascld.org/lab). ~http://www.aafs.org/employ/brochure1.htm#Criminalistics

How bullet imbalance causes a lateral drift velocity which causes deflection of the bullet trajectory as it leaves the muzzle. http://home.snafu.de/l.moeller/Geschosse/Bullet_Imbalance.html

The left sketch shows how the Center of Gravity (CG), offset from the center line or geometric axis, is forced to rotate about the geometric axis.

This is an unnatural condition This is an unnatural condition. A spinning projectile will always spin about its principal axis and the principal axis always passes through the projectile CG. Consequently, when it exits the muzzle, it will start to spin about its principal axis and CG. While the bullet is in the bore, the CG offset produces a tangential velocity component (Vt). When it exits the bore, this Vt will as a Vd be maintained. The lateral drift velocity will be perpendicular to the plane containing both the geometric and principal axes at the instant of muzzle exit, obtained the distance, that the bullet will deflect, by multiplying the lateral drift velocity by the flight time (FT).

The equation that calculates the amount of bullet deflection at the target is: http://home.snafu.de/l.moeller/Geschosse/Bullet_Imbalance.html

Experimental Evaluation This figure shows 4 3-shot groups formed by indexing the bullets in 90 degree increments in roll angle. The bullets had a large CG offset c’0.00118 in. The experiment determined the radius of dispersion at 100 yards was about 2.5 inches. http://home.snafu.de/l.moeller/Geschosse/Bullet_Imbalance.html

This CG offset value was determined by the diameter and length of the hole drilled in the side of the Bullet, used in the experiment that follows. Let's calculate the dispersion radius to be expected at 100 yards from this oversize CG offset.  s = 24*3.14159*(2900/10)*0.1*0.00118 = 2.58 inches

Gravity vs. the bullets velocity and spin…

Then… if there is wind…