Internal, External, and Terminal Ballistics
BALLISTICS originated from the Greek word “Ballein”, which means ‘to throw’, and from the Roman word “Ballista”, which means ‘a machine to hurl a stone.’
Ballistics is defined as the study of projectiles and the factors affecting them. The science of ballistics has been developed to facilitate the examination of firearms; ammunition matters related to it. Ballistics is divided into three major types that include internal ballistics, external ballistics, and terminal ballistics.
Colonel Godard first coined forensic ballistics. He used the systematic study of firearms and ammunition in the commission of the crime for investigation and identification.
The three major classifications are discussed below in detail.
Internal ballistics deals with the study of incidents happening within the barrel of a weapon from when the firing pin hits the primer to the time the bullet exits from the barrel. It deals with:
- The scratch marks produced on the projectile while passing through the barrel. This helps in linking the projectile with the firearm.
- The velocity of the projectile. a projectile acquires proper ballistics only if it’s manufactured to match the barrel.
- Defects in barrel.
- The cause of erratic behavior of projectiles.
Factors affecting internal ballistics are
- Barrel– It provides space for the various process involved in the firing of the cartridge. It provides helical lands and grooves to impart spin to moving projectiles.
- Length of the barrel– If the length of the barrel is long, the propellant is consumed before the projectile reaches the muzzle end of the firearm.
- Bore characteristics– The bore of the barrel corresponds to the diameter of the bullet, which should seal the bore.
- Muzzle of the barrel– The muzzle end can seriously affect the projectile’s trajectory if it’s asymmetric.
- Energy transfer– A projectile acquires energy from the gases produced from the burning of the propellant.
- Rifling– The lands and grooves of the barrel create resistance to the movement of the projectiles.
- Chamber– The size of the chamber has to correspond to the size of the cartridge.
- Recoil– The firing of a firearm propels the projectile / ejects forward with a specific force. The process pushes back the firearm with equal momentum.
Deals with the traits of the motion of the projectiles after leaving the muzzle, namely trajectory, velocity, range penetration, etc.
External ballistics studies the flight of the bullet from the muzzle of the weapon to the target. This subject involves parameters such as bullet shape, sectional density, atmospheric pressure.
Factors affecting external ballistics.
- Spin– The speed of the spin varies with the twist of the rifling in the barrel.
- Drift– Side way shift of the projectile from the line of departure. It takes the direction of the spin.
- The formula gives sectional density of a projectile.
SD = w/ d2
Where w is the weight of the projectile and d2 is the square of the cross-sectional diameter.
The efficiency of the flight of the projectile dramatically depends upon its sectional density.
- Ballistic Coefficient – The ballistic coefficient is denoted by C. It is the index of the ability of the projectile to overcome air resistance.
- Air resistance– It retards or accelerates the velocity of the projectile.
It deals with the study of the behavior of the missile once it reaches the target. It defines the traits of the impact of projectiles on the target.
If the target is living tissue, it is known as wound ballistics.
Terminal ballistics is concerned with the study of penetration potential and wound ballistics.
Penetration potential is the capability of the missile or the projectile to penetrate the target. It depends upon the type of surface of the impact of the projectile, the thickness, flaccidity, the depth of penetration, and the volume of the cavities.
The pieces of evidence related to firearms are used to study the bullet hole, powder, or shot pattern on clothing, on the body, or on any other objects for determining the direction range of firing of the gun.
It is, therefore, necessary for all police officers entrusted with the investigation of firearms cases to understand the characteristics of firearms and ammunition and their evidentiary values in crimes.