Category Archives: Forensic Ballistics

Forensic Ballistics, Forensic Science

Cartridge Cases

INTRODUCTION

These are almost invariably made of brass with a 75 : 25 copper/zinc alloy. Other materials including steel and plastic have been used, but not on any commercial basis. Shotgun cartridges generally have a brass base with a plastic, or sometimes paper, case.

PURPOSE

  • The main purpose of the cartridge case, other than for holding the components together, is to expand and seal the chamber during firing. This is called ‘obturation ’ and prevents the explosive escape of high-pressure gases through the breech.
  • During manufacture, the brass is annealed to give the case the correct degree of hardness.
  • If this is correct, the brass will regain its original shape after the pressure has subsided and the case will be easy to extract from the chamber.
  • If it is too hard, the case will crack, and if too soft, it will cling to the chamber walls and be extremely difficult to remove.

Cartridge Case Types

1. Straight Cased

Where the case diameter is approximately the same along its length.

2. Bottle – Necked

Where a wide – bodied case is, just before the case mouth, reduced in diameter to that of the bullet. This permits a very much larger volume of propellant to be used, and consequently higher velocities to be obtained, than in straight – sided cases.

3. Tapered case

Where a wide – based cartridge case is gradually reduced in diameter along its length. These tend to be in old European sporting rifle calibres and are seldom encountered.

According to the configuration of cartridge case base, it’s subdivided into five categories :

(i) Rimmed

These have a flange at the base which is larger than the diameter of the body of the cartridge case. This flange is to enable the cartridge to be extracted from the weapon in which it is used. When describing rifle ammunition and the metric method of designating the ammunition is used, these are often identified by an ‘ R ’ after the case length measurement, that is, 7 × 57 mmR. The vast majority of revolvers are designed for use with rimmed ammunition.

(ii) Semi – rimmed

These have a flange which is slightly larger than the diameter of the cartridge case and a groove around the case body just in front of the flange. When describing rifle ammunition and the metric system is used, these are identified by ‘ SR ’ in the cartridge designation.

(iii) Rimless

In these, the flange diameter is the same as the case body and there is, for extraction purposes, a groove around the case body just in front of the flange. There is generally no letter system to designate this cartridge base type. Self – loading pistols are almost invariably designed for use with semi – rimmed or rimless ammunition.

(iv) Rebated

This has an extractor flange which is less than the diameter of the cartridge case. The designation used in the metric system is ‘ RB ’ . This type of cartridge case configuration tends to be reserved for high – powered cannon ammunition.

(V) BELTED CASE

These have a pronounced raised belt encircling the base of the cartridge. This belt is for additional strength in high – pressure cartridges.

The metric designation is ‘ B ’ . This type of cartridge case is generally only found in very high – powered rifle cartridges or military cannon ammunition.

Forensic Ballistics, Forensic Science

BLACK POWDER (GUN POWDER)

What is Black Powder?

Black Powder also known as Gun powder, that burns rapidly, producing volumes of hot solids and gases which can be used as a Blasting Powder and a Propellant for Firearms, Rockets, and Fireworks.

Composition of Black Powder (Gun Powder)

Charcoal and Sulfur act as the fuel for the explosion, while Potassium Nitrate acts as an oxidizer.

75% Potassium Nitrate (KNO3)

Potassium nitrate / Saltpeter / Niter, an oxidizing agent is a substance that provides Oxygen (O2) for the combustion of some other components.

15% Charcoal (C)

Charcoal is used (instead of pure carbon) because it contains incompletely decomposed cellulose.

10% Sulfur (S)

Sulphur is used for reducing the ignition temperature of Charcoal.

How Does Gun Powder Work After Ignition?

At the point When the Black Powder is ignited, the Carbon and Sulfur consume quickly to produce Carbon Dioxide (CO2) and Sulfur Dioxide (SO2). Simultaneously, the Potassium Nitrate decomposes to produce a variety of products, one of which is Nitric Oxide (NO). The rapid formation of very hot gases is responsible for the shock wave produced in the explosion.

Is Black Powder and Gun Powder is Same?

They are slightly different from each other. Black Powder invented  in 19th century while Gun powder is much more older than Black Powder. Black Powder produces less smoke than Gun Powder.

What Was The Use Of Black Powder?

Black Powder used as a propellant in Firearms, Rockets, Fireworks and, Artillery. Black Powder also used as a explosive in Mining and Road building.

Is Black  Powder Still Used?

Black Powder is no longer used in modern firearms or weapons.

What Is Gunpowder Used For Today?

At present, the powder is used in Grenades, Rockets, Guns etc. Generally, Gunpowder is used for Military purposes.

Where Was Black Powder Invented?

Black powder is believed to have originated in China. An author “Wei Boyang” wrote about gunpowder in his book “Kinship of the Three”, (a translation of “Cantong qi”), he wrote about the chemical composition of  gunpowder and the experiments conducted by alchemists was also described.

What Powder Is Used In Modern Cartridge?

Modern Cartridge contains smokeless powder which contains Nitrocellulose (Single base powder), Nitroglycerine (Double base powder), and sometimes Nitroglycerine and Nitroguanidine (Triple base powder).

Forensic Ballistics, Forensic Science, MCQs

Multiple Choice Questions on Forensic Ballistics

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Knowledge Makes You Strong Internally.

Archana Singh
Forensic Ballistics, Forensic Science

FORENSICS BALLISTICS

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What is Forensic Ballistics?

Forensic ballistic is the examination of evidence relating to firearms at a crime scene, which studies ballistic speed, mobility, angular movement, and the effects of projectile units, such as; bullets, missiles, and bombs.

Who is a Father of Forensic Ballistics?

Calvin Hooker Goddard is known as a father of forensic ballistic.

He was a forensic scientist, army officer, academic, researcher and a pioneer in forensic ballistics.

What Can Ballistics Determine?

Forensic ballistic determines :-

  • Which type of gun uses by the criminal?
  • Whether the gun is associated with any other crime?
  • The amount of damage a bullet can inflict.
  • Estimate the position of shooter by analyzing the bullet marks.
  • From which angle the gun was fired?
  • When the gun was fired?
  • The type of impact made by bullet.
  • To reveal the shooter’s identity.
  • Comparison of different firearm, bullets, and, cartridge cases.

Who is Ballistics Expert?

A forensic ballistics expert is who matches, analyzes and examines bullets, cartridges, fragments, and other evidence with the weapons of alleged suspects or others involved in a case.

The first case of forensic firearm examination

The first case of forensic firearm examination was done and documented in 1835. That was when Henry Herbert Goddard applied ballistic fingerprinting to link a bullet recovered from the victim to the actual culprit. After careful  inspection of bullet he found that there was a deformation on the surface of the slug that was not because of barrel or by the impact. It appeared as a manufacturing defect. He understood that retrieving the shot form the weapon would help him easily confirm the shooter. When the suspect’s house was checked, a mold was found at his house.  the marks on the mold and the mark on the bullet matched completely after comparison. Finally he confessed his crime.

 Basic Theory Of Firearm Mechanism

The weapon aims to convert chemical energy into kinetic energy in order to expel a projectile from the firearm.

Firearm Mechanism

The Mechanism is :

A round consists of an outer cartridge case, a bullet, some form of propellant, and a percussion cap is first loaded and locked into the breach.

The firing pin is generally mechanically restrained and, when the firearm is cocked, the firing pin spring is compressed.

As the trigger is pulled, the hammer-mounted firing pin is forced forward to strike through a small hole in the breech face, hitting the primer cup (contains a mixture of sensitive chemicals), which rapidly burn and produce sufficient hot gases to ignite the propellant.

As the gunpowder is ignited an expansion of gas occurs which, confined in a small space, eventually forces the bullet down the barrel of the firearm.

Types Of Ballistics

  • Internal Ballistics
  • External Ballistics
  • Terminal Ballistics
  • Transitional Ballistics

Internal Ballistics – Internal ballistic is about Motion of the projectile in the bore of the weapon.

External Ballistics – External Ballistic is about Motion of the projectile from muzzle end of the barrel to the target.

Terminal Ballistics– Terminal Ballistics also known as Wound Ballistics. It deals with the effect of projectile on the target.

Transitional Ballistics– It deals with the motion of the projectile from the time it leaves the muzzle until the pressure behind the projectile is equalized.

Types of Firearm

Revolver – Revolver is a Handgun that has a cylinder with holes to contain the cartridges. The cylinder revolves to bring the cartridge into position to be fired.

Rifle – Essentially a long rifled barrel firearm primarily designed for relatively long range use in warfare or hunting. Rifles are available as single shot, self-loading, manual action, bolt action or automatic, though most commonly encountered are self-loading.

Submachine Gun – A fast-loading weapon with a high rate of fire, available as single shot or fully automatic. The inaccurate SMG is a magazine-fed weapon which can hold up to around 100 rounds, designed for continuous fire.

Machine Gun – A machine gun is a fully-automatic firearm. This has a very high rate of fire with a fast reload time and great power. They are generally only used by the military.

Shotgun – A shoulder-fired long gun with no rifling in the barrel, designed to shoot a large number of small projectiles (“shot”) rather than a single large projectile (“a bullet”).

Pistols – Pistols are firearms designed for a more automatic operation. Cartridges are loaded into an ammunition magazine which is inserted into the firearm.

Other – Other types include:

  • Air Guns,
  • Gas Guns,
  • Antique Guns,
  • Light Weapons, Etc.

Examination Of Bullets

CLASS CHARACTERISTICS

The make and model of the weapon can also be inferred from the combination of different class characteristics that are common to specific manufactures. The three main class characteristics of all bullets are the :

  • Lands And Grooves,
  • The Caliber Of The Bullet,
  • And The Rifling Twist.

Lands are the raised portions between the grooves inside the barrel after the spiral grooves are cut to produce the  rifling.

In firearms, caliber is the specified nominal internal diameter of the barrel.

Rifling twist refers to the rifling in the barrel of modern rifles making a full 360 degree rotation in a given length of inches.

INDIVIDUAL CHARACTERISTICS

These random imperfections or irregularities can be produced by:

  • Manufacture
  • Wear from Abuse
  • Wear from Use

The striations on the bullet can make identifiable and unique markings that trace it back to a particular firearm.

How Good a Match is It?

The theory behind firearm identification is that microscopic striations and impressions left on bullets and cartridge cases are unique, reproducible, and therefore, like “ballistic fingerprints” that can be used to identify a gun. If investigators recover bullets or cartridge cases from a crime scene, forensic examiners can test-fire a suspect’s gun to see if it produces ballistic fingerprints that match the evidence.

Ballistic Fingerprinting – Ballistic fingerprinting refers to a set of forensic techniques that rely on marks that firearms leave on bullets to match a bullet to the gun it was fired with.

THE COMPARISON MICROSCOPE

The comparison microscope is a most important tool for firearm examination.

Two bullets can be observed and compared at the same time within the same field of view.