SEMINAR

DEPARTMENT OF FORENSIC MEDICINE

Presenter: Dr (Maj) Manoj BalachandranPost Graduate

FIREARMS AND EXPLOSIVE INJURIES

CONTENTS1. Definition2. Parts of a firearm3. Classification & types4. Shot guns and rifled arms5. Cartridges 6. Powders, bullets7. Ballistics 8. Tests for GSR9. Entry and exit wounds10. Explosion injuries11. Medico-legal importance

DEFINITION A firearm is any weapon which discharges a

missile by the expansive force of the gases produced by burning of an explosive substance.

To produce an efficient firearm, there are three basic criteria to be met.

Weapon should be capable of causing substantial damage

It should be reliable & convenient to use It should be reasonably accurate

PARTS OF A FIREARM1. Barrel

1. Chamber2. Taper3. Bore

2. Action3. Grip

CLASSIFICATION1. Rifled weapons2. Smooth bore weaponsAccording to firing action:3. Over-bolt action4. Under-bolt action5. Lever action6. Pump action or auto loading model

Rifled weapons Rifles, air and gas-operated rifles, 0.22

rifles, military and sporting rifles, single shot target practice pistols, revolvers, automatic pistols, true automatic weapons (machine guns).

Smooth- bored weapons (shotgun) Cylinder bore, choke bore, paradox

(hammered, hammerless), breech loader, muzzle loader, country made.

CHOKING OF A FIREARM

AIR WEAPON (AIR RIFLE) Fired single small lead pellets or lightly

feathered darts by means of compressed atmospheric air.

SHOT GUNS One/double barreled version The calibre of large shotgun is expressed

according to their bore or barrel diameter usually 16 bore or 12 bore.

The size of the bore is determined by the number of lead spheres.

Each of the lead sphere will precisely fit the barrel that can be made from 1lb of lead.

The main powder varies with different makes of ammunition but nitrocellulose or nitroglycerine is usually incorporated.

Note: The collective term for all injuries caused by

firearms is “gun-shot wounds”. When the wounds are caused specifically by a

popular sporting weapon such as a 12 bore shotgun “A shot gun wound” should be used.

TYPES OF FIREARMS Rifle- A relatively long-barreled firearm, fired

from the shoulder, having a series of spiral grooves cut inside the barrel (a process called ‘rifling’) imparting a rapid spin to a single projectile.

Shotgun- A shoulder-fired long gun with no rifling in the barrel, designed to shoot a large number of small projectiles (“shot”) rather than a single large projectile (“a bullet”).

Machine gun- A machine gun is a fully-automatic firearm. This means the weapon will continue to load and fire ammunition until the trigger, or other activating device, is released, the ammunition is exhausted, or the firearm is jammed.

Sub-machine gun- A hand-held, lightweight machine gun consisting of relatively low-energy handgun type cartridges and fired from the hand, hip or shoulder.

A revolver is a firearm that has a cylinder with a number of chambers. These chambers are designed to be manually loaded with cartridges of the appropriate caliber and then, as the cylinder rotates into position under the hammer, the trigger can be pulled, releasing the hammer causing the cartridge to be fired.

Pistols are firearms designed for a more automatic operation. Cartridges are loaded into an ammunition magazine which is inserted into the firearm.

As long as cartridges are present in the ammunition magazine and the firearm is functioning properly, the action of the firearm is responsible for the feeding and chambering of the cartridge and the extraction and ejection of the cartridge case once the cartridge is fired. They can be designed to fire semi-automatically or fully automatic.

Semi-automatic operation requires a pull of the trigger to fire each cartridge. Fully automatic operation allows for multiple cartridges to be fired with a single trigger pull for as long as ammunition is available to be fired

Craft weapons: according to Small Arms Survey, “craft production of small arms refers principally to weapons and ammunition that are fabricated largely by hand in relatively small quantities.

Craft produced small arms range from rudimentary pistols and shotguns to more advanced assault rifles.” The homemade guns are included in this category. Homemade guns are crude firearms roughly made from basic, household materials.

Other types include air, gas, and antique guns, light weapons, etc.

SHOTGUNS Type I < 5 m ;

the pellets strike the target as a single mass, resulting in massive kinetic energy transfer and

tissue avulsion high mortality rate (85–90%)

Type II injuries (5–12 m) ; usually result in much less tissue destruction. there is significant dispersal of the pellets and loss

of energy.

SHOTGUN WOUNDS AT VARYING DISTANCES

Penetration may occur through deep fascia, but fractures are rare. Ocular injuries can occur as well as embolization of lead pellets,mortality rate (15–20%)

3. Type III injuries > 12 m usually only the skin is penetrated mortality is rare (0–5%)

RIFLED ARMS These include the revolver, the automatic pistol, the machine gun and the service and sporting rifles. They all discharge a single projectile or a bullet. The weapons may fire the bullets simply or in rapid fire depending on the mechanism. The purpose of the rifling system.

Spin the bullet around its longitudinal axis stability in-flight

Resisting tendency for the bullet to change its altitude. Penetrating power

RIFLED CARTRIDGE•Cartridge cases ( outer covering of the cartridge) are made up of Cardboard & plastic.•Bullet cases are made of brass (70% copper and 30% zinc).

•A few have a nickel coating. •Primer cases are of similar composition (Cu-Zn). •Bullet cores are most often lead and antimony, with a very few having a ferrous alloy core.•Bullet jackets are usually brass (90% copper with 10% zinc), but some are a ferrous alloy and some are aluminum. •Some bullet coatings may also contain nickel (Ravreby, 1982)

SHOT GUN CARTRIDGE

• Short metal cylinder which is continuous with a cardboard or plastic cylinder. • The case is rimmed which helps to keep the cartridge in correct position in the chamber and makes extraction easy.• Length of cartridge varies from 5 to 7 cm.• The cartridge case: Percussion cap, gun powder, retaining cardboard disc.• Power piston- four leaflets or petals

PRIMER The major primer elements are Lead styphnate

(Pb), Barium nitrate (Ba), or a Antimony sulphide(Sb). Usually, all three are present.

Less common elements include Aluminum (Al), Sulfur (S), Tin (Sn), Calcium (Ca), Potassium (K), Chlorine (Cl), or Silicon (Si).

Primer elements may be easier to detect in residues because they do not get as hot as the powder, and compounds (not just elements) may be detectable.

BLACK POWDER POTASSIUM NITRATE OR SALT PETER - 75% CHARCOAL- 15% SULPHUR- 10% Charcoal is the fuel, potassium nitrate the oxygen

supplier gives the mixture more density and makes it more readily ignitable

Smokeless powder- nitrocellulose (single base), nitroglycerine and nitrocellulose (double base) or nitrocellulose, nitroglycerine and nitroguanidine (triple base)

Semi-smokeless powder- 80% of black + 20% smokeless

BULLETS The traditional bullet- soft metal and has a

rounded nose. In rifle – elongated pointed end Mushroom bullets, short flat point, medium

flat point, pencil point, streamlined with sabot. Jacketed and semi-jacketed bullets Dumdum bullet- fragments extensively Frangible bullet- completely disintegrate Explosive bullets, tracer bullets, plastic bullets

BALLISTICS

Knowledge of physical forces acting on the projectile & missile Interior Ballistics Exterior Ballistics Terminal / Wound Ballistics

INTERIOR BALLISTICS

Knowledge of the forces responsible for propulsion of projectile within the bore of the barrel till the end of the projectile

Exterior (external) ballistics It refers to the attributes and

movements of the bullet after it has left the gun muzzle, which includes the condition of the bullets’ movement and flight up to the target.

TERMINAL BALLISTICS It refers to the effects of the impact of the

projectile in the target. The knocking power of particular powder load of the cartridges which makes a devastating lesion, caused by the bullet.

Forensic ballistics It refers to the investigation and identification of

firearms by means of ammunition fired through them. This is the real branch of the science which the police use as their guide in field investigations.

Shot ballistics- It is the study of shotgun ammunition including its characteristics spread and trailing.

Wound ballistics- It refers to the study of the effects of a projectile on a target and the conditions that affect them

Tattooing- They pierce under the superficial skin layers causing punctate abrasions of smaller blood vessels under the skin

Gross splitting: Seen in high velocity bullet & contact wound of low velocity bullet . Tail wag/range/gas penetration. BLOW BACK PHENOMENON

Bruising (at or around entry wound due to general tissue trauma) MUZZLE IMPRINT, Gases of the blast ballooning & bruising the skin/Vital reaction / Inflammatory reaction

Abrasion Collar: Raw rub of the superficial skin layers while projectile enters the skin. More prominent in rifled firearms due to their rotational motion

TESTS TO DETECT GUNSHOT RESIDUES

Scanning electron microscopy Energy dispersive X ray spectrometry “Case by case” Romolo and Margot Scientific Working Group – USA ENFSI EWG Firearms/ GSR Working

Group- Europe

CLASSIFICATION OF GUNSHOT ACCORDING TO VELOCITY

low velocity ( < 350 m/s )

Intermediate velocity (350–600 m/s)

high velocity (> 600 m/s)

CHARACTERISTICS OF ENTRY AND EXIT WOUNDS OF A RIFLED WEAPON

Entry wounds The dimensions will vary with the calibre of the weapon1. A Contact Wound

- May be split, scorched, blackened and the muzzle area soiled with partly burned powder.- Tissues may be bruised by blast or blown away.

2. A Near Discharge- Within arm’s reach but over 15 cm.- Show split entry hole and scattered tattooing by powder markings

3. A More Distant Discharge- The entry hole is split by tail wag of the bullet.

Exit wounds The exit wound will show merely a hole in the skin torn

to a degree dependant upon the momentum of the bullet, the amount of bone splinter it carried with it, distance of wounding

The soiling ring will distinguish entry from exit wound. At close range, the entry wound is larger than the exit

because being split by blast (exception the bullet comes out sideways or carrying bone with it)

At more distant range the exit and entry are the same size (unless the bullet is deflected by bone)

X-ray – facilitate a search for a lost bullet

MEDICO LEGAL CONSIDERATIONS (RECONSTRUCTION)

The questions the doctor will be expected to answer are:

1. Could the wound have been inflicted with that weapon.

2. At what range was it fired?3. From what direction?4. Could it have been self-inflicted?

EXPLOSION INJURIESDisruptive effectsAir blast (shock wave)Effect of blast wave/shock waveBurnsFlying missilesFalling masonryFumes Blast wave of the explosion : 1) Positive phase: very high pressure travelling faster than the speed of air last for few milliseconds 2) Negative phase : low pressure of longer duration

Also the blast wave (shock wave) has “spalling“ effect when it passes from one medium to another of less density which cause the medium to spall “fragments“

So the shock wave can damage in three ways :1. Hydrostatic pressure of the shock (positive

phase)2. Dynamic pressure of the shock which follow the

hydrostatic pressure behind it (negative phase).3. Spalling effect

TYPES OF EXPLOSION WOUNDS Non-penetrating : grazing or blast wound

Penetrating : low impact velocity ,bullet does not exit

Perforating : high velocity , bullet in and out

Avulsive : massive wounds with avulsion and loss of tissues .

MEDICOLEGAL IMPORTANCE Usually accidental Homicidal cases rare Reconstruction- type, severity and

distribution of injuries upon the body Relative position of the bomb and the

victim

REFERENCES1. The essentials of Forensic medicine

and Toxicology- Dr K S Nararyan Reddy- 33RD edition

2. Textbook of Forensic medicine and Toxicology- Principles and Practice- Krishan Vij- 6th edition

3. PPTs from the internet