Tag Archives: forensic ballistics

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.

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).