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The physical forces that determine the wounding potential of gunshot and other penetrating wounds
- Wounding potential of bullet is determined by mass and velocity.
- The type and severity of a wound is determined by:
- Wounding potential
- Construction and shape of the bullet
- Orientation of the bullet upon striking body
- Deformity or fragmentation
- What tissues the bullet traverse
- Traditional distinction between low and high muzzle velocity does not differentiate kind and severity of wounding:
- A civilian hunting rifle or a large-caliber handgun with a hollow-point bullet may produce a more severe wound than a bullet with a full metal jacket from a “high-velocity” military rifle.
- Bullets wound by 2 main mechanisms—crush and stretch:
- Sonic pressure wave that precedes bullet has no role in wounding.
- Bullet crushes the tissue it directly passes through, forming a permanent cavity.
- Stretch is produced by radial energy transferred from bullet as it slows down in tissue, forming a temporary cavity.
- A bullet is stabilized in flight by spin transmitted from rifling in the barrel.
- Spin minimizes yaw, which is the angle between the long axis of the bullet and its flight vector.
- Without spin, a bullet would yaw to its most stable flight configuration, which is base and center of mass forward:
- Not aerodynamically efficient
- As bullet enters tissue, spin of bullet is reduced and bullet will yaw.
- When yaw is 90°, a bullet crushes maximal amount of tissue, slows down the most, and maximal stretch injury occurs.
- Bullets designed to deform in tissue (soft point, hollow point) will expand on impact:
- Increases amount of crush injury
- Moves bullet center of mass forward
- Jacketed bullets prevent lead stripping in the barrel, which occurs at high muzzle velocities:
- Jacketed bullets do not deform but may fragment.
- Fragmentation increases surface area and crush injury.
- Bullets striking bone often fragment and may cause bone fragments to become secondary projectiles.
- Severity of wound also depends upon tissue composition and thickness:
- Minimally elastic tissues, near-water-density tissue (brain, liver), fluid-filled (heart, bowel) and dense organs (bone) may be injured by the temporary cavity.
- More elastic tissue, such as lung and skeletal muscle, may absorb the energy from temporary cavity formation and sustain minimal damage.
- Extremities are often not thick enough for the bullet to fully yaw:
- Temporary cavity formation is minimal.
- Most damage is caused by direct crush injury of the bullet, its fragments, or secondary projectiles.
- Short-range shotgun blasts can produce severe wounds with compromise of the blood supply:
- In short-range shotgun injuries, pellets may be greatly scattered in tissue secondary to the pellets striking each other.
- Stab wounds with knives and other sharp instruments are low-energy wounds with tissue injury from direct weapon contact.