Saturday, August 25, 2012

Bullet effects

 Not too surprisingly, a lot of our apocalyptic fiction involves gunfire.  So the little details of what is (supposed to be) actually going on are of interest to me.

The linked study deals with a lot of the basics of firearms, as it would pertain to you medical practitioner (presumably a coroner) attempting to determine the cause of death, and describe the injuries.

I have pulled out the small section on what are the primary inputs into causing injuries with modern firearms.  Be forewarned, these report is a medical report, and the wound illustrations are very graphic.

J. Scott Denton, Adrienne Segovia, and James A. Filkins, Practical Pathology of Gunshot Wounds, 2006.
Obviously, the anatomic location of the wound is critical - a gunshot wound to the central nervous system, even one of low velocity, can be more life threatening than ahigh-velocity wound through the arm. Involvement of vital structures such as the heart, aorta, lung, liver, spleen, and kidneys can quickly lead to hemorrhage, hypoxia, and death. Tissue damage is not, however, limited to the paththe bullet travels through the body. Damage may occurremote from the bullet path if the kinetic energy of thebullet is great enough to produce a shock wave. Cavitary effect is the concept that explains the shock wave produced by a bullet as it passes through an organ or otheranatomical structure.

As a bullet passes through a bodyand transfers its kinetic energy, it produces a shock wave that creates a temporary cavity greater than the bullet’s diameter. The greater the kinetic energy that is transferred the greater the size of the temporary cavity. Velocity is more significant than mass in determining kinetic energy; therefore, cavitary effect is more pronounced in injuries from high-velocity ammunition. The extent of damage depends on whether the transient expansion of tissues and organs exceeds the elasticity of the particular structure through which the bullet passes. Organs such as the liver and spleen, which lack elasticity, are easily lacerated. Organs that are more elastic, such as the stomach and intestines, may only suffer contusions. After the temporary cavity collapses, a permanent cavity wider than the bullet may persist (Figure 9).

Note that the study agrees with what I have seen of detailed examinations of the issue.  Shot placement is the number one factor, and velocity (and energy in general) is also a factor as the body temporarily balloons out from the bullets shock wave.   Note however, this shock wave is also rather placement dependent, so the idea that bigger bullets make bigger holes also has its merit.

The study, for obvious reasons, doesn't address non-common injuries.  I suspect if they saw a lot of them, the large low velocity, but erratic but tumbling shot gun slug, like the earlier musket- and mini-balls would do more damage than modern high velocity rounds.  Likewise, if they were using bow and arrow fire out there, I suspect that the clean slicing arrows would be about as effective as medium caliber pistol rounds.  That is about how effective they appear to be in the frontier accounts I have read in any case.

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