WOUND BALLISTICS

definition

Ballistics: the flight characteristics of a projectile

Projectile: an object fired from a gun with an explosive propelling charge, such as a bullet, shell, rocket, or grenade.

Ballistics of firearm

1. Internal (travel within the gun)2. External (gun to target)3. Terminal (wound ballistics)

The guns

1. Handgunsa)Single shot weapons (target pistol)b)Derringerc)Revolverd)Semi-automatic pistol

2. Rifles3. Shotguns4. Fully automatic

Target pistol Derringer

Revolver Semi automatic pistol

Rifle

Shotgun

Fully automatic gun

Myths and Mechanisms of Firearm Injuries

ActionChamber

Barrel

Rifling

Bore

Caliber

Muzzle

HammerMagazine(Clip)

Anatomy of the Gun

Myths and Mechanisms of Firearm Injuries

Anatomy of the Cartridge

ShotgunHandgun Rifle

Primer

Flash Hole

Powder

bullet

Powder

Primer

Wad

Shot

1. Internal ballistics• What happens when the trigger is pulled?1. Primer fires2. Intense flame created by primer fills chamber3. Powder burns, creates large gas expansion4. Huge pressure generated pushes bullet

• The more complete and instant the burning, the more efficient the expansion of gas

• The tighter the hold of the bullet in the cartridge, the tighter the fit in the bore the more efficient use of the gas

2. External ballistics

• Gun to target

The physics of ballistics

Newtonian physics:• Kinetic energy• Newton’s law of motionLaw of inertiaLaw of accelerationLaw of reciprocal action

Law of conservation of energy

Kinetic energy

Newton’s law of motion1. Law of inertia:An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

2. Law of accelerationThe acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

3. Law of reciprocal actionTo every action there is always an equal and opposite reaction

The law of conservation of energyEnergy may neither be created nor destroyed. Therefore the sum of all the energies in the system is a constant.

3. Terminal ballistics (wound ballistics)

Bullets produce damage in 3 ways:1. Laceration and crushing2. Cavitation:

a) permanent cavityb) temporary cavity (tissue splash)

3. (Shock waves)

Wound potential The tissue damage a moving bullet can cause,

determined by the missile mass and velocity

• Bullet construction (diameter, shape, mass and velocity of the projectile)

• Physical properties of the tissue penetrated (tissue elasticity, density, cohesiveness, internal architecture)

Bullet penetration depth is directly related to bullet mass and bullet velocity, and inversely related to bullet diameter

Mechanisms of wounding

1. Crush the crushing of the tissue struck by the projectile (forming the permanent cavity)

2. Stretch the radial stretching of the projectile path walls (during temporary cavity formation)

The sonic pressure wave preceding the bullet through tissue does not damage tissue

Crushing of tissue

• A missile crushes the tissue it strikes, thereby creating the permanent cavity.

• Yaw the angle between the longitudinal axis of the bullet and its path of flight

• Expansion when striking soft tissue with sufficient velocity, soft point and hollow-point bullets are designed to deform at the tip into a mushroom shape

• Overexpansion can result in insufficient tissue penetration to reach and disrupt vital structures

• Fragmentation Bullets of the hollow-point or soft-point variety are more likely to fragment in tissue than a full metal-jacket bullet, adding to tissue disruption

Stretching of tissue

• Fired from an appropriate and well designed firearm, a bullet flies in the air with its nose pointed forward and it yaws only 1° to 5°.

• It is stabilized in this point-forward position by bullet spin imparted by the rifling (spiral grooves) in the gun barrel

• It’s spin is not adequate to stabilize it in a point-forward position in tissue, because of the higher density of tissue relative to the air

Myths and Mechanisms of Firearm Injuries

ActionChamber

Barrel

Rifling

Bore

Caliber

Muzzle

HammerMagazine(Clip)

Anatomy of the Gun

• After the bullet crushes its maximal amount of tissue, it is slowed down rapidly, as its wounding potential is used up moving tissue radially away from its path. This force creates the temporary cavity

• In tissue, this temporary cavity can produce injury from localized blunt trauma if it is large enough to stretch the tissue and displaces beyond its breaking point.

• Near-water-density, less elastic tissue (such as brain, liver or spleen), fluid-filled organs (including the heart, bladder or fluid-filled intestine) and dense tissue (such as bone) may be damaged severely, when a large temporary cavity contacts them or forms within them.

• More elastic tissue (such as skeletal muscle) and lower-density elastic tissue (such as lung) are less affected by the formation of a temporary cavity

The effect of the passage of a bullet through tissue

• Because of the skin's toughness and elastic properties, a bullet might be arrested subcutaneously at the end of the wound path.

• Bullets can be caught below the scalp or subcutaneously in the rest of the body

• Handgun wounds of the extremities yield characteristic fracture patterns

• The magnitude of bone fragmentation depends on the amount of pressure generated within the bone

• Bone fragments (secondary missiles) also crush tissue

• Divot fractures removal of a divot-hike portion of the edge of a bone, always involving the cortex and occasionally some adjacent medullary bone

• Drill-hole fractures cylindrical core of bone removed by the bullet

• Spiral fractures common in bones under torsional stress at the time of bullet impact

The effect of the trauma• In penetrating trauma, the tissue is crushed throughout the

length of the hole• In blunt trauma, organs with inadequate tissue cohesiveness

to tolerate displacement will fracture and tear• Complete or partial vascular occlusion can occur, when intimal

injury and intravascular thrombus result from penetrating trauma or rarely, when tearing of the vessel results from tissue displacement (blunt trauma)

Role of medical officers

• Evaluate and document wounds before they are distorted by surgical intervention.

• Must resist temptation to make assumptions about findings

interpretations are correct in only 47% of cases • Do not describe wound as “entrance” or “exit”

without indicating physical features of each.• Must provide complete documentation of all

wounds

Entrance wound

Divided into 4 general categories according to range of fire:1. Contact2. Close Range3. Medium Range4. Indeterminate

• When examining entrance wounds, remember The size of entrance wounds bears no relationship to the caliber of bullet that inflicted it.

1. Contact wound

• All material (bullet, gases, soot, metal fragments) is driven into the wound

• Muzzle contusion

2. Close range

• Distance of less than 6 inches • Dispersion of soot (which can be wiped away)

3. Intermediate range• Generally found at distances of 60 cm or less

• Tattooing is pathognomonic

Tattooing cannot be wiped away (soot can)

Density of tattooing is dependent on the distance & caliber

4. Distant range- No tattooing or deposition of soot - Indentation of skin creates Abrasion coll

friction between bullet and skin (not caused by heat of bullet.

palms and soles won’t have abrasion collars.

Angle of impact depends on shape

Cannot determine distance

Exit wound

• Skin edges are generally everted • Abrasion collars and soot are not

usually associated with exit wounds

• Tattooing is never seen at an exit wound

• Are NOT always larger than its corresponding entrance wound

• May not appear directly opposite the entrance wound.

Other evidence• Opportunity to recognize, preserve, or collect short-lived

evidence.

• Clothing can provide important information.

Therefore, place each item in its own separate paper bag.

• Every bullet and jacket has its own “fingerprint”

• Try not to obliterate these marking by removing a bullet with hemostats or pickups

References

• Wound Ballistics: Analysis of Blunt and Penetrating Trauma Mechanisms, Health Science Journal, 2010

• Ballistics for Physician: Myths about Ballistics and Gunshot Injuries, Santucci.R; Chang.Y