Ballistics is the science that deals with the launching, flight, behavior, and effects of projectiles. A projectile can include anything that can be launched by physical or mechanical means, such as a rock, baseball, spear, arrow, bullet, or missile. In this article, we will discuss basic of ballistic trauma, mostly as caused from small arms fire.
Knowledge of the trauma caused by bullets is not only useful in extreme survival scenarios or on the battlefield, but also for hunters and those in law enforcement. It is also very useful for the medic to understand the type of injury they may be called upon to treat.
High-velocity projectile damage as caused by a bullet is, as you might imagine, much greater than low-velocity damage caused by, say, a knife wound. This damage depends on the amount of energy the projectile possesses due to its motion. In physics, this is referred to as kinetic energy. It follows the formula:
Kinetic Energy = mass of the projectile times its velocity squared, divided by 2. or KE = mv2/2
The “square” of a number is the number multiplied by itself, for example, the square of 2 is 2 x 2, or 4. Because of this, you can see from the formula that the velocity, or speed, of the projectile is more important in the causing of damage than its weight, or mass.
As a missile passes through tissue, it decelerates, transferring all of this kinetic energy to living tissue. The result is a traumatic wound caused by several methods:
• Permanent Cavitation: the path permanently left by the projectile. Essentially, this is the bullet hole and the channel caused by its traverse through the body.
• Temporary Cavitation: A wider shock wave which crushes tissues beyond the actual path of the bullet. This is caused by the dissipation of kinetic energy as the missile decelerates when it meets resistance. Although various organs have differing elasticities, the shock wave surpasses the tissue’s ability to absorb the energy involved, causing damage.
• Deformation: As the bullet enters the body, it may deform, increasing its diameter and the cavity it causes, often at the expense of penetration depth. Hollow point bullets are an example of projectiles that are meant to deform (“mushroom”) as they travel through the body.
• Yaw: Yaw refers to the rotation of the nose of the bullet away from the line of flight. A short, high velocity bullet begins to yaw more severely and turn upon entering tissue. This causes a larger temporary cavitation and more tissue to be violently displaced.
• Fragmentation: Bullets may fragment as they travel through the body. This causes multiple cavitation channels, both permanent and temporary. Some bullets are specifically designed to fragment for this very purpose.
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In future articles, we’ll discuss the different ballistic trauma characteristics of rifle, handgun, and shotgun wounds, as well as basics of treating these wounds. To see the supplies that Nurse Amy feels are important for the medic in these situations, check out her comprehensive video below:
Joe Alton, M.D.
