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Chapter: Forensic Medicine: Firearm injuries

Firearm injuries

Firearm injuries
Although firearms also include arms that can fire plastic and rubber bullets, as well as industrial nailguns, it is especially pistols, revolvers and rifles which are important.

Firearm injuries

Introduction

Although firearms also include arms that can fire plastic and rubber bullets, as well as industrial nailguns, it is especially pistols, revolvers and rifles which are important. This group of firearms is divided into handarms and shoulderarms, and also according to whether the barrel is rifled or not. Rifled firearms have spiral grooves on the inner surface of the barrel which gives the spinning movement to the projectile as it travels down the barrel. This rotational movement or spin stabilises the projectile in flight. Handarms, for example revolvers and pistols, as well as shoulderarms such as hunting rifles, and automatic and semi-automatic machine guns, all have these grooves. Smooth-bore firearms (eg shotguns) do not have grooves.

When the percussion pin activated by the trigger strikes the percussion cap, the spark generated ignites the propellant powder in the bullet casing. This powder has chemical and physical characteristics peculiar to the type of ammunition. The gases which develop during the explosion have a potential volume many times greater than that of the powder, generally in excess of 500 times under atmospheric pressure. It is this gas pressure which drives the projectile along the barrel. While passing along the barrel the projectile is soiled by oil and gas in the barrel. When it leaves the muzzle there is also a flash and a gas emission, which includes carbon monoxide, as well as hot and partially unignited powder particles, all of which impart to the recipient surface characteristics which assist in determining the firing range for that particular weapon and its ammunition.

Although the medical practitioner is not a ballistics expert the observations made in the case of firearm injuries can be of considerable assistance in establishing the range as well as the direction of fire, the type and calibre of weapon and the nature of the wound, for example whether it points at suicide, homicide or an accident. Then, and equally relevant, there is the establishment of (in the case of fatal injury) the manner of death as well as the period of survival and the extent of immobilisation of the victim and restriction of volitional acts on account of the injury.

 

In order to measure up to the expectations of the court in this regard, close attention must be paid to the size and shape of the entrance and exit wound(s). Careful inspection of the skin around the entrance wound, noting the presence, size and shape of any abrasion collar, smoke blackening, tattooing and singeing of hair, is an essential element of the medical investigation. Evidence should also be sought of any vital reaction, such as erythema (a reddening of the skin) in the vicinity of hot-powder tattooing and carboxyhaemoglobin in surrounding tissues (carbon monoxide is one of the gases emitted by the explosion in the chamber of the firearm).

An X-ray examination of the body (both at the clinical examination and the autopsy) can be of considerable assistance in retrieving projectiles for ballistic examination, particularly in the case of multiple entrance wounds.

In siting both entrance and exit wounds it is helpful if measurements are expressed as the perpendicular height above the base of the heel line. Entrance and exit wounds must preferably be indicated on a diagram. This can assist (when evidence is given) to relate the findings to circumstantial evidence. It must be remembered that the direction of the wound track, with the body in the anatomical position during the post-mortem examination, is not necessarily representative of the position of the body when it was hit by the projectile. For instance, if the individual was slightly bent over while running away, and then hit by a projectile fired at a horizontal level, the entrance wound in the back may be lower than the exit wound at the front if the body is in the anatomical position.

Caution should be exercised when expressing an opinion on the pre-impact direction of the projectile flight path based solely on the wound in the tissues after impact, as there can be considerable deflection, not only through the bony structures, but also through the soft tissues.

During clinical examination and autopsy other evidence should be sought, such as powder marks on the hands of the victim and assailant and other evidence of a struggle by either party. Clothing can absorb much of the explosion residue and modify the shape of the entrance wound. Therefore it should always form an integral part of the examination. Serious omissions in the accumulation of medical evidence may result where no attempt is made to anticipate the needs and priorities of the subsequent inquiry. This is what happened initially at the autopsy of President Kennedy after his assassination. (See Where Death Delights by Milton Helpern.)


Multiple firearm wounds do not necessarily rule out suicide. In one case the deceased had three separate revolver wounds in the chest and all three bullets had penetrated the ventricles of the heart. A suicide note was found, the revolver was shown ballistically to have fired the shots, and swabs taken from the deceased's right hand contained the specific powder residue.

The percussion effect set up in the tissue by shock waves during the projectile's flight is well exemplified in the following case. A fugitive who was running away from the scene of a burglary, was fired on at a range of about 40 metres while his trunk was flexed forward in a position customarily adopted by escapees to reduce the target site. Despite being hit by a shot, he continued to run for another 100 metres, before collapsing. He died half an hour later. At the autopsy an entrance wound was indentified above the left iliac crest, on the lateral side of the body. The bullet had tracked upward in the subcutaneous tissues to enter the chest cavity between the eighth and ninth ribs, and had then passed across the dome of the diaphragm, below the parietal pleura, along the outer aspect of the pericardial sac to come to rest in the apex of the left lung.

Neither the abdominal cavity nor the pericardial sac had been penetrated by the projectile, yet the former contained 100 ml of free blood and the pericardial sac 350 ml of blood, resulting from a 2 cm percussion rupture of the liver, and 3 cm rupture of the left ventricle of the heart .


 


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