Ammunition

Introduction

Ammunition in forensic ballistics refers to cartridges made up of Shells, Propellants, Primers, and Projectiles that are regularly used in weapons.

Ammunition is defined as any ordnance that can be used in combat or warfare, according to section 2-1 (b) of the Indian Act of 1959.

It includes:

  • Rockets, Bombs, Grenades, And Other Live Missiles
  • Articles Designed For Torpedo Service And Submarine Mining
  • Other Articles Containing Or Designed Or Adapted To Contain Explosive, Fulminating, Or Fissionable Material Or Noxious Liquid, Gas.
  • Firearms Charges And Related Accessories
  • Fuses and friction tubes

Parts of and Machinery for Manufacturing Ammunition

Most of the crimes committed involve the use of small arms, which consists of :

(i) Cartridges

(ii) Propellants

(iii) Primers

(iv) Projectiles

(v) Wads

Small Arms

Small arms ammunition is of two types. These are:

  • Metallic ammunition
  • Shotgun ammunition

Components of metallic cartridges are:

(i) Metallic cartridge case (shell or empty)

(ii) Percussion cap or primer

(iii) Propellant (or gun powder)

Bullet Shotgun cartridges have the following components:

(i) Paper cartridge case (shell or empty)

(ii) Percussion cap or primer

(iii) Propellant or gun powder

(iv) Spherical ball or lead pellets

(v) Overshot wad, undershot wad, an air cushion wad, and over powder wad

Cartridge Case

Cartridge cases provide housing for various components of all cartridges. It is usually made of a brass material for rifles, pistols, and revolvers.

Cartridge case must satisfy the following needs:

  • Dimensional specification of chamber
  • It provides for the grip of an extraction
  • Headspace needs
  • It maintains the stability needs of other components after assembly during handling, transit storage, frequent wading, and unloading without any accidental firings.

A Cartridge case is also known as an empty shell.

It is made from several layers of paper which are tightly compressed in the shotgun cartridge case. The base of this paper shell is made of brass. Plastic shells for shotguns are also being manufactured now.

Types of a Cartridge Case:

  • Rimfire cartridge
  • Centrefire cartridge
  • Pinfire cartridge

Rimfire Ammunition

It consists of a short brass tube generally 0.22 inches in diameter and closed at one end. The tube contains a charge of propellant. It has a bullet at the open end. The tube is formed at the closed end into a flat head with a hollow rim. It contains the priming compound.

Centerfire Ammunition

It is generally made from brass. The head is thick and heavy with the central pocket for the primer cap. A hole leading from the primer pocket into the cartridge case. It allows the flash to reach the propellant from the priming compound. Thus, igniting it.

Caseless Ammunition

It consists of a bullet with the propellant. It is formed around the bullet as a single sold piece and there is no cartridge case. The primer is generally located at the rear of the propellant. It is not enclosed in any metallic cup.

Blank Ammunition

It is the same as bulleted ammunition except for the presence of the missile. In blank ammunition, the case mouth is sealed by either metal or inserting a wax plug or paper disc.

Types of the Primer Cup

Berdan Primer Cup

In this system, the anvil is the part of the cartridge case in the form of a small peg in the primer pocket. There are several small flash holes in the cup. It is present around the anvil that permit the passage of ignition flame from the primer to the propellant. This type of primer cup is used in military ammunition.

v

Boxer Primer Cup

In this type of primer, the anvil is a small bent disc of steel that fits into the cup making the primary completely self-contained. The flash hole in the cartridge case is centrally located. It has a large diameter. This type of primer cup is used in commercial ammunition.

Battery Cup Primer

This system consists of a plain cup with no anvil. It fits into a slightly larger inverted flanged cup containing its anvil. The flanged cup provides rigid support for the primer cup and anvil. This self-contained assembly fits into a pocket in the base of the cartridge case. This type of primer is extensively used in shotgun ammunition.

Propellants

(i) The expression propellant means an agent, which fires the projectiles out from a firearm.

(ii) To propel a bullet or shotgun charge through the barrel & air, a certain amount of force is necessary.

The powder charge gets ignited through the primer and converts it into togas very quickly, thereby resulting in the development of high pressure in the cartridge and forcing the bullet to get out of the barrel.

The three types of propellants used are –

(a) Gunpowder (Black powder)

(b) Smokeless powder

(c) Semi-smokeless powder

Gun Powder

Gun powder is the oldest recorded propellant and had been invented by the Chinese around the tenth century. It was used for giving signals and fireworks.

The gun powder consists of potassium nitrate, sulfur, and charcoal roughly in the proportion of 75:15:10.

The powder is not suitable for high-velocity ammunition, as large amounts of powder are required for getting high velocities for the projectiles. The powder leaves a considerable amount of solid residue, which tends to foul the barrel. It remains fairly stable if kept dry, over a prolonged period. It is glazed and polished to increase its storing or keeping qualities. Gunpowder causes much smoke and fouling of the target. It is mostly used in muzzle loading and blank cartridges. The powder is available with different grain sizes- from mesh limit 6-10 to 46-60.

Smokeless Powder

The modern high-velocity era started with the use of smokeless powders. The basic constituents of the smokeless powders are nitroglycerin and nitrocellulose (guncotton).

Nitrocellulose is either used alone or in combination with nitroglycerin to form propellants, the latter are called double-based powders, while the former is known as single-base powder. Some of the double-based powders that are commonly used contain Nitroglycerin. Nitrocellulose and Mineral Jelly are Cordite, modified cordite and Ballistite.

The composition of the common double based powder is detailed below:

Cordite has 58% Nitroglycerine, 37% Nitrocellulose, and 5% Mineral Jelly. Modified Cordite has 30% Nitroglycerine, 65% Nitrocellulose, and 5% Mineral Jelly.

Ballistite has equal quantities of Nitroglycerin and Nitrocellulose without any Mineral Jelly. Smokeless powders degrade with time.

However, the life span of such powder has been increased tremendously by improved technology and by the addition of stabilizers. It is important to note that smokeless powders do not explode inside a cartridge, instead, they combust. Since the combustion is occurring in a closed space, it can have the force of an explosion.

Semi Smokeless Powder

The semi-smokeless powder is a mixture of black powder and nitrocellulose. The approximate composition of the powder is as follows:

Nitrated wood cellulose 20%,

Potassium nitrate 60%,

Carbon 12%,

Sulphur 8%.

This powder produces less smoke than gun powder but the mixing process is quite dangerous. This aspect has prevented its extensive production and use.

Triple Based Powder

The triple based powder contains the following ingredients;

(a)Nitroglycerine

(b)Nitrocellulose

(c)Black powders

RDX Based Propellant

A new propellant in which the active ingredient is from the family of Cyclo-tri-methylene-triamine (RDX) has come up. It is being utilized in the manufacture of cartridges by controlling not only the shattering nature of the high explosive but also its heat production. The advantages are obvious. The rate of fire can be increased without detrimental effect on the weapon firing the ammunition.

An ideal powder should have the following features;

(a) It should be stable on storage

(b) It should not be corrosive

(c) It should produce a minimum amount of smoke

(d) It should produce a minimum amount of heat for a given velocity

(e) It should be homogeneous. The same amount of power should give the same velocities

Primers

The primer composition has the following basic ingredients

(i) An inclinator – a sensitive high explosive

(ii) Fuel

(iii) An oxidizer

(iv) Stabilizer

The sensitive high explosive which functions as an initiator is a pressure-sensitive material that gives out a flame to ignite combustible material which works as a fuel. An oxygen supplier would supply the necessary oxygen so that the combustion of fuel is proper. Friction-causing material is also mixed with to carry out the functioning of the entire exercise in a satisfactory manner.

The basic priming mixture is composed of;

  • Mercury fulminate
  • Stibnite
  • Potassium chlorate
  • Lead azide

In modern times the aforesaid deficiencies have been overcome by the following substitutions;

Potassium chlorate is replaced by barium peroxide and lead peroxide and barium nitrate.

Mercury fulminate is replaced by sulfur, lead, or copper sulpho cyanide with a small addition of trinitrotoluene or tetrol.

Wads

It is used in cartridges basically to keep the projectile and short cartridge in their respective positions and in addition they cease the barrel to prevent the escape of gases and consequently their respective reduction in velocity. It is present in shotgun cartridges, absent in rifles, pistols, revolvers, etc.

In shotgun ammunition, there are several wads.

  • Over-powder wad,
  • Cushion-wad,
  • Under-shot wad
  • Over-shot wad

They keep the charges in the cartridge in their proper places. In addition, the cushion wads seal the barrel on firing and thus prevent the escape of gases and consequent loss of velocity. They also clean and lubricate the barrels. The overshot wad which is waxed also keeps away the moisture. The overshot was kept in position by crimping the edges of the cartridge or by turning the edge inside.

Some manufacturers cover the projectile with star-shaped crimping only.

An innovation of great importance in the structure of wads is the power piston wad.

It is a single plastic structure consisting of three parts;

  • Rectangular sleeve
  • A cushion
  • An overturned cup, like an overpowered device.

The power piston wad has an advantage over the conventional wads.

They seal the barrel and prevent the escape of gases from the sides, hence greater power.

The sleeve prevents deformation of the projectiles, hence more uniform patterns are obtained.

In rifled firearm ammunition, the bullet itself seals the mouth of the cartridge case. Sometimes a wad separates the bullet from the powder charge. The wad keeps away the grease placed in the cannelures.

The base, cylindrical surface, and the top wad of a cartridge may carry legend giving its size, type, year of manufacture, and its make. The information is ordinarily in abbreviations which differ with different makes. The information is often important.

Cannelure

It is an indented ring or a series of grooves provided at the base of the bullet around its cylindrical surface. It helps a bullet in getting it firmly seated in a shell or cartridge case.

Lubricants

It provided in cannelure of the cartridge to facilitate the passage of bullet during its movement in the barrel. It also serves as a preservative for projectile and prevents oxidation.

Reference:

Firearms n.d., NCDOJ, <https://ncdoj.gov/crime-lab/firearms-and-tool-mark>.

Ballistics n.d., Human Slaughter Association <https://www.hsa.org.uk/ballistics>.

Ballistics n.d., NIST,, <https://www.nist.gov/ballistics>.

Comparison microscopy n.d., Firearm Examiner Training, <https://projects.nfstc.org/firearms/module07/fir_m07_t08_02.htm>.

Gunshot residue collection n.d., Department of Public Safety Minnesota, <https://dps.mn.gov/divisions/bca/bca-divisions/forensic-science/Pages/forensic-programs-crime-scene-gsr.aspx>.

Examination of Gunshot Residue n.d., The Internet Pathology Laboratory for Medical Education n.d., <https://webpath.med.utah.edu/TUTORIAL/GUNS/GUNGSR.html>.