This blog is useful for students and professionals of Forensic Sciences around the world. Also for Crime Scene Investigators, Jurors, and other law enforcement to keepupdatede with new technologies in Forensic Science, and proactive, investigative,and security forensics.
Friday, December 06, 2019
Introduction to Forensic Ballistics
By Dr. Bhoopesh Kumar Sharma
Forensic Expert & Associate Professor
Introduction to Ballistics:
The term ballistics refers to the science of study of the action, motion and behaviour of a projectile during its flight in any given medium. The flight path of a bullet includes:
•Travel down the barrel (Internal Ballistics),
•Path through the air (External Ballistics), and
•Path through a target (Terminal Ballistics)
Is that branch of forensic science which deals with the examination of the firearm and related evidences encountered at the scene of crime in a shooting incident, and their linkage to the firearm, and Identification of the shooter.
A ballistic expert need to answer the following questions:
Any instrument which is designed or adapted to discharge a projectile or hurl a projectile with the help of force applied by the expanded gases of main charge (propellant). Firearms can be smooth bore, rifled bore, manual/semi-automatic/automatic, handguns, shoulder guns etc.
SMOOTH BORE: -
A gun with a smoothbore (uniform smooth) that shoots cartridges that contain "shot" or small metal pellets (of lead or steel) as the projectiles. The internal diameter of the smooth bore gun is smooth and have no grooving inside the barrel.
For Example: - Shot guns and country made firearms
RIFLED BORE: -
These contain rifling (grooving) in their barrel. The spiral grooves cut inside a gun barrel that give the bullet a spinning motion. The metal between the grooves is called a "land".
For Example : - Rifles, Revolver, Pistols, Machine Guns etc.
Rifling provides a steady uniform and gyratory (spinning) motion to the projectile during flight. The gyratory motion has two important effects on the bullet :
•It stabilizes the bullet flight with nose on position
•Increases the effective range of firing
•It decreases the air resistance.
Cartridge= Primer + Main Charge + Projectile + Cartridge Case
An Ammunition is the assembly of primary charge (also known as primer/initiator or detonator, usually high explosives), the main charge (also known as the gun powder or propellant), the projectile (may be in the form of shots/pellets or single bullet), and the case or shell.
IDENTIFICATION & INDIVIDUALIZATION OF FIREARM
Basic Principle: -
No two firearms, even those of the same make and model, will produce the same unique marks on fired bullets and cartridge cases. Manufacturing processes, use, and abuse leave surface characteristics within the firearm that cannot be exactly reproduced in other firearms.
All cases that involve firearms identification start with preliminary examinations of the evidence for similar class characteristics and different Individual Characteristics.
Class characteristics can be defined as:
Intentional or design characteristics that would be common to a particular group or family of items.
The class characteristics of firearms that relate to the bullets fired from them includes the caliber of the firearm and the rifling pattern contained in the barrel of the firearm.
Cartridges and Cartridge cases on the other hand are examined for class similarities in what are called breech marks, firing pin impressions, extractor marks, ejector marks and others.
Individual characteristics can be defined as:
marks produced by the random imperfections or irregularities of tool surfaces. These random imperfections or irregularities are produced incidental to manufacture and/or caused by use, corrosion, or damage. They are unique to that tool and distinguish it from all other tools.
RANGE OF FIRING (Distance of Firing)
Estimation of Range of firing totally depends upon the deposition of the Gun Shot Residue (GSR) over the wound.
The projectile comes out from the muzzle along with the EJECTA
Each Ejecta particle (flame, smoke etc) is a having a certain distance of traveling from the muzzle which depends upon the following: -
•Nature of Firearm (Smooth bored/ Rifled bore)
•Nature of Ammunition (Black Powder/Semi smokeless Powder/Smokeless Powder)
•Nature of the Target
•Caliber of the Firearm
•Length of the Barrel
But as an average for the Standard Firearm the approximate distance for different ejecta particle is as follows: -
In case of Shotguns: -
•Smoke travels up to a distance of 30 cm
•Flame up to 45 cm
•Partially burnt & un-burnt particles up to a distance of 60-90 cm
•Wads up to 2-5 meters
•Shots are dispersed according to distance
In case of rifled weapons:-
•Smoke up to 30 cm
•Flame up to 8 cm
•Powder grains & metallic chips up to 60-90 cm
Each and every ejecta particle is responsible for different phenomena over the gun shot wound (firearm injury) as follows: -
•Smoke produces Blackening or Smudging over the wound
•Flame is responsible for Burning of Skin, Scorching and Singeing of hairs
•Partially burnt or un burnt powder grains are responsible for Tattooing
•The projectile is responsible for the collaring (contusion collar/Grease collar/abrasion collar)
The Science of Forensic Ballistics is of great significance in solving the shooting cases and helps the law enforcement agencies to answer the questions required for the proceedings of the case in the court of Law. Forensic Ballistic can answer: -
nIs the injury caused by discharge of firearm.
nWhat kind of weapon fired the shot.
nWhat was the possible distance (range) of firing.