Presentation on theme: "Ballistics By the end of this unit you will be able to:"— Presentation transcript:
1 Ballistics By the end of this unit you will be able to: Explain the differences between a handgun, a rifle, and a shotgunKnow the series of events in the gun which cause the bullet to leave the barrel.Describe unique markings that may be used to identify bullets or guns used in cases.Lands and groovesRiflingFiring pin impressions
2 BallisticsDescribe how bullets are test fired and matched in the laboratoryDiscuss the role of ballistics recovery and examination at a crime sceneDetermine the position of the shooter based on bullet trajectory
3 Introduction Ballistic evidence helps explain: What type of firearm was usedThe caliber of the bulletThe number of bullets firedWhere the shooter was locatedWhether a weapon was fired recentlyIf a firearm was used in previous crimes
4 Review Firearms and Rifling Grooves and ridges (lands) in the barrel of a gun produce the twisting that adds accuracyThis leaves a pattern on the bullet that is unique
5 Review: Bullets, Cartridges, and Calibers Cartridge—a case that holds a bullet, primer powder, and gunpowderThe bullet, usually of metal, is out front with the cartridge, holding the primer and propellant powders, behind.
6 Review: How a Firearm Works The firing pin hits the base of the cartridge, igniting the primer powderThe primer powder sparks through the flash hole to the main propellant supplyThe pressure of the explosion pushes the bullet from the casing into the barrelThe bullet follows the lands and grooves spiraling out of the barrel
7 Caliber of the Cartridge Caliber—a measure of the diameter of the cartridgeIn hundredths of an inchCommon calibers include .22, .25, .357, .38, .44, and .45Why should the caliber of ammunition match the firearm that shoots it?If they do not match, what could go wrong?
8 Review: The Study of Bullets and Cartridge Casings How is each fired bullet marked?What is the procedure to match a spent bullet to the firearm that shot it?What makes up a test-firing, and why is it done?
9 Review: Marks on the Spent Cartridge Casings Evidence found at a crime sceneFiring pin marksappear on the rim or center of the spent cartridgecan be used to match a cartridge to a firearm
10 IBIS Integrated Ballistic Identification System Program controlled by the ATF (Bureau of Alcohol, Tobacco, & Firearms)Software and program which produces a digital history of bullets,casing,and cartridges.FBI and ATF joined forces and use a super powered computer now to track ballistic evidence left at crime scenes.
11 Gunshot Residues Gunshot Residues (GSR) Particles of unburned powder and traces of smokeLeave traces on the hand, arm, face, hair, or clothing of the shooter and/or victimHot gasses may cause burnsChemical testing can detect residue even if removal is attempted3 elements :lead, antimony, & barium; all 3 must be present to be used in court
12 How a spectrophotometer works Spectrophotometer is the name of a machine which can identify elements and the amounts of each element to create a spectrum chart.Location on X-axis ID’s type of elementHeight of peak shows concentration
13 Distance Identification Distance from victim to shooter can be determined by examining the residue pattern on the victimIf muzzle touches victim: burns, powder and partial bullet fragments will be imbedded into wound. Blood and tissue back backsplash onto gun or shooter.At a distance, less powder and burning occurs to victim.Powder will coat clothing and hands of shooter but can be washed off. This is why crime scene investigator tape brown bags over the hands.
14 Wound Patterns Entry wounds Smaller than exit wounds Entry wounds can pull fibers into bodyIf close contact= star shaped or shredded appearanceDistance very neat entry woundCan be difficult if bullet ricochets off boneCaliber and velocity affect wound appearance
15 Trajectory Two reference points are needed to define the trajectory Investigators can figure the shooter discharged the firearm somewhere along that line
16 Trajectory Reference points can be bullet holes in objects or victimsAn entry point and exit point on a victimGunshot residue or spent cartridge casingsLasers can trace a straight-line path to determine the position of the shooter
17 Trajectory and Gravity Bullet’s path is slightly curvedGravity pulls it downward as the bullet moves forwardDiagram is highly exaggerated
18 Determining the Location of the Shooter Building is 60 feet away along the horizon lineBullet hole is 4 feet above the groundWhere is the shooter located?
19 How to read a right triangle Sine, Cosine and Tangent are all based on a Right-Angled Triangle"Opposite" is opposite to the angle θ"Adjacent" is adjacent (next to) to the angle θ"Hypotenuse" is the long oneAdjacent is always next to the angleAnd Opposite is opposite the angle
21 Example: find the height of side d Start with:sin 39° = opposite/hypotenuse = d/30Swap Sides:d/30 = sin 39°Use a calculator to find sin 39°:d/30 = …Multiply both sides by 30:d = … x 30 = to 2 decimal places.
Your consent to our cookies if you continue to use this website.