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Forensics: Ballistics Notes
Transcript of Forensics: Ballistics Notes
Created by: Erin, Monae, Natalie, and Xena
Study of projectile's behavior when it hits the target.
Study of the projectile's behavior between the time it leaves the barrel and its airtime before it hits an object
Study of the projectile's behavior once it leaves the barrel
“The identification of fired bullets, cartridge cases or other ammunition components as having been fired from a specific firearm”, as scientists like to put it, which means the action of analyzing firearm usage in crimes.
Study of the projectile's within the gun's barrel
Important concept is the amount of damage done to the target by the blast effect and flying small pieces of a shell or bomb.
The study of terminal ballistics helps scientists to make more effective weapons and to devise means of defense against enemy weapons.
The projectile has a spinning motion which keeps it at a stable flight through the air.
While in the air, the projectile has to beware of various forces, such as gravity, air resistance, wind, and drift
Regulating pressure created from the gas produced ignited by the powder within the barrel is an important problem in internal ballistics.
Too little pressure = The bullet won't reach it's target
Too much pressure = gun blowing up
Varying pressure = velocity of bullet changes and accuracy is poor
Also known as intermediate ballistics
Most modern pistols, revolvers, rifles, and some shotgun barrels have grooves cut or formed in a spiral nature, lengthwise down the barrel of a firearm.
This is how the spin by the bullet is done.
The lands are the raised areas between two grooves. A rifling pattern of eight grooves with also have eight lands.
History of rifling and 3 Methods of Rifling
Broach method of rifling uses a hardened steel rod with several cutting rings spaced down the rod. The rod is twisted as it is pulled through the barrel and this forms the spiral to the rifling pattern.
With button rifling s a very hard steel plug is forced down an unrifled barrel. The grooves are then formed in the barrel under very high pressure. The pressure created to form the rifling in the barrel hardens and polishes the inside of the barrel.
Hammer forging produces a type of rifling called polygonal rifling. A hardened steel mandrel is produced with the shape of the rifling formed on its outer surface. The mandrel is inserted into a barrel blank and is hammered. The hammering forces the barrel material down against the mandrel and the inner surface of the barrel takes on the shape of the mandrel.
Every firearm leaves unique identifying characteristics on the bullet and the cartridge during the firing process.
Forensic ballistics involves:
Analysis of bullets and bullet impacts to determine the type of bullet and gun.
Studies GSR, bombs with their trajectory, angle, marks and importance in a crime
Parts of a gun
Measurements of a gun
Holding a gun
Firing a gun
End of the firearm that is held by an individual
Grip or Butt
(in rifles and shotguns)
Breach: The Breach is the area of the firearm that contains the rear end of the barrel, where the cartridge is inserted.
Trigger: The Trigger is the lever that’s pulled or squeezed to initiate the firing process.
Muzzle: The muzzle of a gun is the front end of the barrel where the projectile exits the firearm.
Magazine: A Magazine is a spring-operated container, that can be fixed or detachable, which holds cartridges for a repeating firearm.
Hammer: The Hammer on a revolver is the part that strikes the firing pin or the cartridge primer directly, detonating the primer which discharges the gun.
Range: The longest distance a gun can fire a bullet
The width of the internal part of a gun barrel or the diameter of the bullet.
The width of the barrel of the gun
Recorded in hundredths of an inch or millimeters. Ex .22,.38,9mm.
Not exact measurement.
Bullet casing wider than the slug *in some situations*
Caliber does not equal the length or power of the bullet
• Higher the gauge number = the smaller the barrel’s diameter.
• 12- gauge shotgun = diameter of 0.730
• 16- gauge = .670
• Calculated as the number of lead balls of a bore diameter required to make up one pound.
Most common shotgun gauge= 12
• Bore diameter = 18- 18.5mm
• Powerful, used for large games/ self defense
2nd most comment = 20 gauge
• Less powerful, used for smaller game
• Bore diameter = 15.6mm
Caliber vs. Gauge explained by professionals
Markings are caused by the bullet passing through the barrel of a gun.
Rifling creates a unique blueprint in the barrel for the markings (grooves, direction, spirals, etc) found on the bullet
Microscopes are used to observe the microscopic striations
On October of 2002, two men, John Allen Muhammad and Lee Boyd Malvo
murdered 10 and critically injured 3 people with a Bushmaster .223-caliber rifle
Using a magazine that was dropped at a crime scene the FBI was able to pull a fingerprint matching Lee Boyd Malvo's fingerprint, and that ATF confirmed that Muhammad owned a Bushmaster .223 rifle illegally. The rifle, scope, and tripod used in the shootings were found in Muhammad's car. The ATF was then able to do ballistic analysis on the gun and the bullets to prove that this was the gun used in eight of the ten killings.
How did they do it?
Maps were found showing the exact location of each attack
They created a setup for the attacks in Muhammad's blue Chevy sedan.
Components of a firearm projectile
Gunshot residue (GSR) is a type of physical trace evidence that is released when a gun is fired and may directly place an individual at the scene of weapons discharge. Examined in crime investigations on peoples' hands or clothing. Extremely useful in determining the potential suspects or known victims
Ballistics & Crime
Inside the barrel
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