Ballistics 2

Lecture 2

types of ballistics

Internal

external

terminal

Internal ballistics

Concept deals with whatever happens within the barrel of a weapon from the moment the firing pin hits the primer to the time the bullets exits from the barrel.

It is mainly concerned with propellant pressures, acceleration of the missile whilst it is in the bore, muzzle velocity and recoil.

Parts of a bullet

Primer, igniter, propellant charge, driving band, bursting charge, booster, detonator, blackpowder, fuse and time-train rings

Ignition and pressure

The firing pin strikes the primer cup, crushing the priming compound (e.g., lead styphnate), which initiates a flame jet.

Propellant burn

Gases: Propellant (smokeless powder) burns rapidly, producing large volumes of high-pressure, hot gases (up to 50,000 psi and 2000∘ C).

Chamber Pressure: This pressure determines the acceleration rate of the bullet and the overall muzzle velocity.

Engraving & travel

Engraving: The bullet base obturates (expands) to seal the bore, and the lands and grooves cut into the bullet's surface, imparting spin.

Rifling Twist: The direction and rate of the spiral twist (e.g., right-hand twist) are class characteristics of the barrel.

Muzzle blast and recoil

Muzzle Flash/Blast: Unburnt gases and powder exit the barrel, creating the flash and sound.

Recoil: The action/reaction (Newton's Third Law) force applied back to the weapon mechanism and the shooter.

External ballistics

It deals with the flight of the bullet from the muzzle of the weapon to the target.

two main factors that affect the trajectory

air resistance

gravity

The exact shape of this trajectory can be predetermined by knowing:

gravitational effect

muzzle velocity

angle of elevation of the barrel

sectional density of the bullet

bullet shape.

Trajectory

Parabolic Path: The bullet follows a downward-curving path due to gravity and air resistance.

Line of Sight vs. Line of Departure: The sights are aligned to compensate for bullet drop over a specific range (sight height/zeroing).

Air resistance

Drag: The force slowing the bullet down. It is proportional to the square of the velocity, meaning bullets slow down much faster at higher speeds.

Ballistic Coefficient: A measure of a bullet's ability to overcome air resistance. Higher BC means better long-range performance.

Stability (spin)

Gyroscopic Stability: The rifling- induced spin prevents the bullet from tumbling end-over-end (yaw) during flight.

Precession & Nutation: Minor circular and nodding movements of the bullet's nose as it stabilizes.

Drift

Rotational Drift (Coriolis Effect): The spin causes the bullet to slowly drift perpendicular to its line of flight (usually minor for short ranges).

Terminal ballistics

It deals with the behavior of the missile once it reaches the target.

Penetration & deformation

Penetration Depth: The distance the bullet travels into the medium. It depends on bullet kinetic energy, mass, velocity, and shape.

Expansion/Fragmentation: Soft- point or hollow-point bullets are designed to mushroom upon impact, increasing the frontal surface area and creating a larger wound.

Wound ballistics

Permanent Cavity: The direct path of crushed and destroyed tissue left by the bullet (the track itself).

Temporary Cavity: The stretching and displacement of elastic tissue surrounding the permanent cavity, caused by the transfer of kinetic energy.

Ricochet and deflection

Angle of Impact: If the angle is very shallow, the bullet may skip or glance off a surface (ricochet).

Medium Density: Impact on intermediate objects (like glass, wood, or clothing) can cause deflection, altering the trajectory before the main target.

Transfer of energy

Kinetic Energy Loss: The energy transferred from the bullet to the target medium, primarily responsible for the destructive effect.

Toolmark analysis

any mark left on an object (like a cartridge case or bullet) by the mechanical action of a tool (the firearm components).

Comparative microscopy

allows two items (e.g., a crime scene bullet and a test- fired bullet) to be viewed simultaneously to compare unique striations and marks.

Firearm class characteristics

Caliber (e.g., 9mm), number of lands and grooves, direction of twist (left or right), width of lands and grooves.

Database systems

Automated Ballistics Identification Systems (ABIS) use specialized optics and software to capture and compare the unique marks on fired bullets and cartridge cases against large databases.

Gunshot residue (GSR)

Microscopic particles containing characteristic elements (Lead, Barium, Antimony) that originate from the primer compound.