FSCI5560 - Ballistics Flashcards

Key terminology in ballistics lecture notes.

Firearm

A lethal barrelled weapon capable of discharging a projectile with kinetic energy greater than one joule.

Caliber

The internal diameter of a firearm barrel, also used to refer to the diameter of the bullet that fits into the barrel. Metric = (5.56)mm. Imperial = (0.223)”. Caliber= (223)cal.

Rifling

The spiral grooves formed in the barrel of a firearm that cause the bullet to spin for improved accuracy and stability.

Gunshot Residue (GSR)

Particles or residues discharged from a firearm after the trigger has been pulled, potentially including chemicals from the primer and propellant.

Muzzle flash

The visible light emitted when a firearm is discharged, typically caused by the ignition of gunpowder as it exits the barrel.

Ballistics

The study of the dynamics of projectiles, including their motion and effects upon impact.

Semi-automatic mechanism

A firearm mechanism that automatically chambers the next round but requires a trigger pull for each shot.

Bullet trajectory

The path that a bullet follows from the firearm to its target.

Gunshot Residue Analysis

The forensic analysis of residue to associate a suspect with the discharge of a firearm.

Suppressor

An attachment for a firearm that reduces the noise level of the gunshot when fired.

Shotgun choke

A constriction at the end of the shotgun barrel that helps to control the spread of the shot as it leaves the barrel.

Recoil

The backward movement of a firearm when discharged, caused by the reaction to the force of the bullet being propelled forward.

Flash hider

A device attached to the muzzle of a firearm designed to minimize the visibility of the muzzle flash.

Cartridge

A single unit of ammunition consisting of a casing, primer, propellant, and bullet.

Breech Loader

Weapon in which the ammunition is inserted into the rear of the barrel.

Centre Fire

Ammunition with the priming compound held in a cap in the centre of the base of the cartridge case.

Flash Hole

Hole connecting the priming compound with the propellant charge; also called the vent or touch hole.

Flash Pan

Shallow pan covering the touch hole into which the priming powder is placed.

Muzzle loader

Weapon in which the propellant and ball are loaded from the muzzle.

Primer cap

Small cup containing the priming compound.

Priming powder

Finely divided black powder

Propellant

Solid substance which, when ignited, produces a large quantity of gas to propel a missile down the bore of a weapon.

Rimfire

Self-contained cartridge with the priming compound held in the hollow base flange or rim.

Self-loading

A repeating firearm requiring a separate pull of the trigger for each shot fired. After manually loading the first round from the magazine, the weapon will use the energy of discharge to eject the fired cartridge and load a new cartridge from the magazine into the barrel ready for firing.

A round of ammunition

Modern unit of a firearm ammunition, consisting of: a cartridge case, bullet/projectile, propellant and primer. If the round is too big = jam in battery after firing. if round is too small= will chamber but is ‘loose in battery’- prompt failure of the breech and the gun could explode.

Mass units of propellants and ammunition

GRAIN.

1 gram = 15.4 grains

Class Characteristics

• General firearm class (pistol, rifle, SMG, etc.)

• General dimensions (plus caliber and chambering)

• Make and model

• Shape of firing pin

Can limit an investigation down to the type and class of firearm used, but not the exact firearm.

Individual Characteristics

• Serial numbers: all legally manufactured firearms must carry a serial number. If all components on the firearm do not have the same serial number then it indicates the firearm has undergone modification.

• Proof marks: after having gone through the ‘proofing process’. Process where the unit is stressed around 30% over normal operating procedures. Marks are impressed into the action and other components.

The firing process

1. Primer activation by impact from the firing pin.

2. Propellant starts to burn due to heat coming through flash hole- gas and pressure produced and the cartridges expands (obturates).

3. Pressure becomes sufficient to unseat bullet from the cartridge, launching it down the barrel as the propellant continues to burn.

Rifling terminology

• Lands: raised sections of the barrel wall (hills).

• Land Marks: sunken areas on the surface of a fired bullet.

• Grooves: sunken areas between lands in the barrel wall (valleys).

• Groove marks: raised areas on the surface of a fired bullet.

• Twist direction: rifling can be cut in either left or right hand configuration.

• Twist rate: Tells you how many bullet revolutions per inch of barrel length. (L = C / tan(θ)). remember to convert and round to nearest inch.

• Described angle: angle between the longitudinal bullet axis and inscribed rifling marks (usually less than 10 degrees).

Producing Rifling

• Broach-cut: uses a single point tool to cut one groove at a time, with each groove taking several cuts to each the desired depth.

• Electro-chemical etching: uses an electrolyte, which is passed through grooves in a tool whilst in contact with the inside of the barrel to etch away the material and form the barrel grooves.

• Polygonal rifling- lands and grooves replaced with hills and valleys. Hammer-forged: a tungsten carbide ‘mandrel’. Button-formed: tungsten carbide ‘button’.

Cartridge information

• Protruding rim= Single shot (e.g. revolvers). Parallel sides = self-loading

• Class characteristics: General dimensions/ shape of firing pin mark/ primer type/ headstamp info.

• Individual characteristics: chamber marks, ejection port dent, drag marks, ejector mark.

Jacketing

Stops rifling drag in the barrel at higher velocities.

• Unjacketed: lead alloy only (may be flat, round or hollow nosed), cheap, low muzzle velocity (low penetration, high impact deformation, prone to rifling smear at high muzzle velocities.

• Semi-jacketed: soft point (SP), hollow point (HP) or polymer tipped (PT). Usually a bright bass jacket with a lead alloy core, less impact deformation than unjacketed (low penetration and high energy transfer).

• Fully-jacketed: full metal jacket (FMJ), base can still have exposed lead, usually a bright brass jacket (with a ‘bonded’ or ‘partitioned’ lead alloy core. Excellent penetration with relatively low energy transfer (high stability and high energy retention. More expensive.

Internal bullet structure: solid lead alloy core is most common, partitioned core like a semi-jacketed and FMJ joined together- mushrooms and retains some of its core on impact.