1 What is ballistics? Give examples of how ballistics is used in forensic science.
Introduction Ballistic evidence helps explain: What type of firearm was used. The caliber of the bullet. The number of bullets fired. Where the shooter was. Whether a weapon was fired recently. If a firearm was used in previous crimes. Forensic Science: Fundamentals & Investigations, Chapter 17 2
Firearm Nomenclature Slide Barrel Extracto r Trigger Hammer Safety
Ammunition bsapp.com
Bullets, Cartridges, and Calibers Bullets and cartridges are packaged together. The bullet, usually of metal, is out front with the cartridge, holding the primer and propellant powders, behind. Forensic Science: Fundamentals & Investigations, Chapter 17 5
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Bullet Design “Bullet” refers to the projectile(s) which actually exits the barrel of the gun when fired Bullets vary in shape and composition Most types are variations on three main shapes & three basic compositions bsapp.com
Three Main Shapes bsapp.com
Round Nose Maximum penetration Cheapest to manufacture Easily loads into chambers bsapp.com
Hollow Point Spreads on impact Causes additional damage to target Inhibits penetration bsapp.com
Wad Cutter Used exclusively as a practice load Minimizes penetration Rips a hole in target paper which is visible by the shooter bsapp.com
Three Basic Compositions of Bullets Lead ½ Jacketed Jacketed (Full metal jacket) bsapp.com
Lead CheapDenseSoft Easy to mold bsapp.com
½ Jacketed A lead bullet coated with copper half way up the exposed portion of the bullet Used primarily for hollow points hollow points Copper improves exit velocity exit velocity Lead promotes mushrooming bsapp.com
Jacketed A lead bullet completely coated in copper Copper improves exit velocity Used to hold the shape of the bullet in an effort to maximize penetration bsapp.com
Caliber of the Cartridge Caliber is a measure the diameter of the cartridge in hundredths of an inch. Common calibers include.22,.25,.357,.38,.44, and.45. Why should the caliber of ammunition match the firearm that shoots it? If they do not match, what could go wrong? Forensic Science: Fundamentals & Investigations, Chapter 17 18
What happens to bullets when they are fired? bsapp.com
Pull the Trigger and... 1.A pin strikes the primer causing a spark. 2.The powder is then ignited causing an explosion. 3.This explosion pushes the bullet down the barrel bsapp.com
Down the Barrel 4.As a bullet travels down the barrel, it is twisted by the lands and grooves of the barrel. bsapp.com
Out of the Barrel 5.This rifling causes the bullet to exit in a spiral motion bsapp.com
Bullet Analysis & Comparison What are some characteristics used to identify & compare bullets? bsapp.com
Striations bsapp.com
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Matching Procedure Fire bullets from a suspected weapon With the aid of a comparison microscope, compare these “test fires” to the suspected bullets Striations must be identical for a positive match bsapp.com
Comparison Microscope Two scopes- One Field bsapp.com
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What happens to a bullet when it hits a target? Most bullets tend to mushroom when they hit a target.Most bullets tend to mushroom when they hit a target. Some bullets nearly disintegrate.Some bullets nearly disintegrate. Left are bullet fragments from a ½ jacketed hollow point.Left are bullet fragments from a ½ jacketed hollow point. bsapp.com
Not all bullets mushroom the same. A lot depends on the speed and shape of the bullet, and the characteristics of the target. bsapp.com
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Some more bullets recovered after firing The striations from the rifling are still visible bsapp.com
Gunshot Residues Chemical testing often can detect gun shot residue even if removal is attempted. What does this mean for investigation? Forensic Science: Fundamentals & Investigations, Chapter 17 37
Databases Like fingerprints, there is a federal database for firearms used in previous crimes – NIBIN (National Integrated Ballistics Network). Forensic Science: Fundamentals & Investigations, Chapter 17 38