MISSILE INJURIES – High velocity missile wounding using military projectiles1

In   Issue .

This paper discusses  high velocity missile wounding caused  by military projectiles. For the purpose of this paper, military projectiles considered will be those of eight mm  diameter or less, fired from small arms like rilles, sub-machine guns  and machine guns. High velocity is defined  as speed in excess of 750 m sec1.

Corporal Martin Andrew

EXPLANATION OF  BALLISTIC TERMS

Rifling
Rifling is the grooves  that are machined inside a barrel, designed to impart a spin on the projectile as it leaves the barreL Rifling imparts  a gyroscopic effect on the projectile, giving it stability in the air. The tighter the twist of the rifling,  the greater  the stability of the projectile, since  the rate of spin is faster. A one-in­ seven  twist is lighter than  a one-in-twelve twist.

Bullet Construction
There arc two main  types of bullet construction in military  projectiles. These are single and dual cores. The single  core uses lead, whereas  dual core uses a combination of lead and another material, usually steeL Projectiles using lead at the rear have improved stability  in flight due to the rear centre of gravity. The jacket  thickness is also important. The  thicker  the jacket, the less likely will the bullet fragment on impact  with  human tissue.  Under international law, all military  projectiles must  have a jacket covering the nose and sides,  hence  the term ‘full metal jacket’

Trajectory
The trajectory of a projectile is the path  the projectile travels through the air until  it impacts  against a surface.  The angle  that a projectile impacts upon  a body is important in wound ballistics. The greater  the impact  angle, the more likely  will the projectile pass through  the body  tangentially.

Drag
Drag is the resistance to movement on an object in a medium. The greater  the density of the medium, the greater  the drag. A projectile upon  entering human soft tissue goes from a medium (air) of 1.2 kg m3 to one of 1,000 to 1,100 kg m3.

Yaw
Yaw is the deviation of a projectile  in its longitudinal axis from the straight line of flight. At close range, under 30 m, high velocity projectiles  exhibit  a large amount of yaw as the stability  effect of rifling has yet to start.  Due to insufficient twist, some projectiles never  become stable in flight, and yaw continually until impact. Yawing determines the surface area of the projectile upon  impact.

Tumbling
Tumbling is the forward rotation around the centre of gravity of a projectile.  Tumbling is determined by a projectile’s  yawing,  drag and design. A greater angle of yaw increases  the drag and promotes quicker tumbling. Dual cores by their nature  cause quicker tumbling. Jacket  construction also contributes to quicker yawing, as a projectile may be more likely  to break up upon  impact.

THE  MECHANICS OF  WOUNDING

The Hague Convention of 1899 stated  that: ‘the contracting parties  agree to abstain  from the use of bullets  which expand or flatten easily in the human body’.

This was subsequently written  into  the 1949 Geneva  Convention. To adhere  to this, all military projectiles  became fully jacketed, and are so to this day. The exception to this is shotgun rounds, which are able to be legally used without a jacket.

When  the Hague Convention  was drafted, nearly all nations went  from round  nosed  to spitzer projectiles, that is, ones with pointed  tips. Round nosed  bullets have poor long range ballistics due  to drag, but excellent penetration on soft tissue as they have minimal yaw, thus also having  poor tumbling characteristics. Spitzer bullets exhibit  better yawing, thus better  tumbling effects on soft tissue.

In all high velocity missile wounding, the two major mechanisms of wounding are cavitation  and  the effect of secondary missiles.

Cavitation

There are two types of cavitation, permanent and temporary.

The permanent cavity is tissue crushed during  a missile’s travel in the body. This is determined by tumbling, bullet deformation, secondary missiles and the missile’s weight upon impact. The greater the penetration and surface area of the missile, the larger the permanent cavity.

The temporary cavity is the momentary stretch  or acceleration of tissue away from the bullet track. It might be thought of as blunt trauma surrounding a portion of a missile’s travel in soft tissue. Elastic tissue like lungs, bowel wall and muscle tolerate stretch much better than non-elastic solid organs like liver, kidneys or a full bladder.

Secondary Missiles

Secondary missiles are objects which perforate tissue away from the main wound  track. These fragments increase the amount of blood vessels injured, tissue perforated and organs damaged. Examples of secondary missiles are bone splinters, missile fragments, zips, buckles, buttons and pieces of hard body armour.

Projectiles can be designed  to break up or fragment. Projectiles such as the German 7.62 x 51 mm NATO bullet, and its Swedish counterpart of the same calibre, have a deliberately thin jacket when compared  to the United States equivalent.  The Australian 7.62 mm round  has a thick jacket similar to the US bullet.

By incorporating  a lead core in the rear of a dual core projectile, it is made stable in flight. Upon hitting tissue, however, it quickly tumbles due to its rear centre of gravity. Dual core rounds also tend to break up at the join of the cores, causing greater wounding with two main wound channels and numerous smaller ones.

Historically, wound ballistic studies have over­ rated  the temporary cavity at the expense of the permanent cavity and secondary missiles. There  arc many variables that affect the temporary cavity size and its effects. These need to be taken into consideration when studying reports about the effects of missiles fired into gelatine blocks simulating human tissue.

The effects of secondary missiles and temporary cavities arc synergistic in high velocity missile wounds. Secondary missiles cause multiple  tissue perforations away from the wound  track, which are then stretched  by the temporary cavity. The weakened tissue splits in many places and pieces of muscle become detached. This creates a larger permanent cavity. At velocities over 900 m sl, in conjunction with  the temporary cavity, secondary missiles cause explosive type wounds, even if bone is not struck. A large, heavy, slow moving missile will have similar effects to a high velocity round, excepting that the permanent cavity is due to the missile’s surface area and weight, not its velocity.

WOUNDING  EFFECTS OF  MILITARY PROJECTILES

To establish the effects of missiles, the then Colonel Fackler at the United States Army Letterman Army Institute of Research, established the Military Trauma Research Division in 1981. He developed the Wound Profile. This is a method  that allows tissue disruption by missiles in soft tissue to be presented graphically. This part of the paper has been written using notes and wound profiles provided  by Dr Fackler when he was in the US Army, Dr Fackler’s work  has removed many of the misconceptions of wound ballistics. The wound profile enables the physician  and researcher to establish why missiles behave differendy at different depths of penetration, without bias. The following wound  profiles describe the military projectiles most likely to be encountered. They describe  the effects of projectiles fired three  metres from a gelatine block.

The 7.62 mm NATO projectile, as used by the Australian Defence Force, and the Russian 7.62 M43 projectile as used  in the SKS and AK 47 family of assault rifles have similar wound profiles. The NATO bullet yaws and causes a large temporary cavity and a medium sized permanent cavity, and ends up travelling backwards. The Russian 7.62 machine gun and sniper projectile is similar, yawing twice with a small permanent cavity initially, and a larger one after it.

Both projectiles  only tumble deep inside the body if soft tissue is involved, and thus cause uncomplicated wounds in most cases of soft tissue injury. In many instances, the Russian projectile only causes wounds  that resemble much lower velocity hand gun wounds. Both the NATO and Russian projectiles have thick jackets and have a forward centre  of gravity which gives them stability in soft tissue.

Comparing the Russian Ml93 and NATO 5.56 mm projectiles, the Ml93 yaws at 90 degrees early in its travel, flattens at the tip, and breaks at the cannelure. The rear of the projectile breaks into multiple fragments. The NATO 5.56 projectile’s tip does not deform, but separates from the rear lead core. This creates two deep wound channels and multiple fragments. Both bullets will break up on contact with soft tissue at up to 200 metres.

The 12-gauge solid slug and 12-gauge number  4 buckshot produce the most devastating close range small arms wounds. In each case the permanent  cavity through soft tissue is 6 em square in cross sectional area. The tissue destruction produced by buckshot is massive when compared  to other small arms projectiles, despite its low velocity, and is a good example of multiple projectile paths in a small area.

CONCLUSION

Much can be learnt of the likely nature and extent of individual wounds by studying experimentally  the effects of various types of projectiles impacting upon synthetic  tissue substances. Detailed graphic analysis of these effects can assist in predicting the threat to troops in an operational environment.