What is ballistics? Give 3 examples of how ballistics is used in forensic science.
Forensic Science: Fundamentals & Investigations, Chapter 17 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
History of Forensic Firearm Identification 1835 – London, England. Mold mark used to make bullet from molten lead used as evidence in homicide case 1863 – Examination of the bullet type and design used to shoot Gen. Stonewall Jackson showed he was shot by one of his own men 1879 – Minnesota. Rifling marks from a revolver used in court to differentiate two revolvers 1925 – The comparison microscope is developed by Philip Gravelle Please refer to the document titled “History of Firearm Identification” by Dr. James Hamby included on the disk for more information and discussion topics.
Forensic Science: Fundamentals & Investigations, Chapter 17
Forensic Science: Fundamentals & Investigations, Chapter 17
Ammunition bsapp.com
Forensic Science: Fundamentals & Investigations, Chapter 17 Parts of a Cartridge Bullets =projectile Case (casing)=holds propellant Cartridge=Bullet+Case Forensic Science: Fundamentals & Investigations, Chapter 17
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Three Main Shapes bsapp.com
Round Nose Maximum penetration Cheapest shape to manufacture Easily loads into chambers bsapp.com
Hollow Point Spreads or mushrooms 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 Cheap Dense Soft 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 Copper improves 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? If they don’t match – the bullet could get stuck or possibly cause the gun to explode/get extremely hot/backfire. Forensic Science: Fundamentals & Investigations, Chapter 17
Firing Sequence bsapp.com
Pull the Trigger and . . . Trigger is pulled, causing hammer to move backwards The hammer strikes the primer. This causes a spark. The powder is then ignited causing an explosion. This explosion starts the bullet down the barrel of the gun bsapp.com
Down the Barrel Rifling inside the barrel causes the bullet to spin, increasing accuracy bsapp.com
Out of the Barrel 5.This rifling causes the marks known as lands and grooves. 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. Some bullets nearly disintegrate. Left are bullet fragments from a ½ jacketed hollow point. bsapp.com
Not all bullets mushroom the same 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
Forensic Science: Fundamentals & Investigations, Chapter 17 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
Forensic Science: Fundamentals & Investigations, Chapter 17 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