Threshold Velocity of Bullet for Penetration of Skin/Bones/Flesh

Threshold Velocity of Bullet for Penetration of Skin/Bones/Flesh by Forensic Yard

Penetration potential is the capability of the projectile to penetrate through various materials. Threshold velocity refers to the minimum velocity required by the bullets to penetrate through the skin, flesh, or bones.

When the projectile strikes a human body, the skin, flesh, and bone underneath are depressed and compressed. The continued pressure stretches them beyond the elastic limit, and a hole is created. The stretched skin gains a normal state after the bullet has entered inside. The threshold velocity required to penetrate the skin is about 40-50 meters per second. Therefore, the threshold velocity value for bone penetration is 60 meters per second. 

The bullet continues to travel until it leaves the body through an exit hole, or its energy is spent beforehand.

Wounding Effect of Projectile Depends Upon

1. The Target Site

The human body is not a uniform medium. It consists of 80% water. At places, there are bones, veins, nerves, organs, or blood vessels. Thus the vulnerability of the wounding is not evenly distributed. For example, the injury on the head would be different from the wound that is found on the waist. 

2. The Threshold Velocity

The projectile’s velocity greatly influences the nature and extent of damage caused to the tissues.

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The energy of the projectile is proportional to the square of the speed.

E=1/2 mv2.

If the velocity is doubled, the energy of the projectile becomes four times. The increase in mass of the projectile also increases its kinetic energy.

The wounding effect can be studied in four threshold velocity zones.

  • Velocity under 400 m/s

In this zone, there is no abnormal wounding phenomenon noticed. The projectile is not deformed or fragmented unless it strikes the bone.

Expanding bullets cause more damage.

  • Velocity Range from 400m/s – 600m/s

Lead bullets and expanding bullets show mushrooming effect at a threshold velocity of 400-600m/s. The extent of deformation dependent on various factors including the striking velocity, the constructional materials, features of the projectile, and the resistance offered by the body.

The tissue damage is more in this case because the cross-sectional area becomes greater as the projectile progresses forward. If the projectile exits the body, the exit hole is observed to be much larger than the entrance wound or the diameter of the body.

  • Threshold Velocity Ranging from 600m/s – 1100m/s

The projectile velocity ranging from 600 to 1100 m/s produces explosive wounds. The high-velocity projectile creates a vacuum behind it. As the projectiles enter the body, the air behind them rushes in at a very high speed to disrupt the body tissue.

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The body part hit by the projectile becomes the secondary missile source causing extensive damage to the body. The projectile, when fragments, creates further damage to the body. As the gyratory motion of the projectiles is very high, the tissue coming into its contact gets torn off. This process inflicts injury on the tissues far beyond the immediate vicinity of the major track of the projectile.

  • Threshold Velocity Ranging Beyond 1100m/s

There are very few cartridges that would propel the cartridges at a speed of 1100 m/s. The effect of the projectile in such cases is the instantaneous death.

3. Constructional Features of Projectile

These features have a good influence on the wounding effect of the projectile. The main determinants of the wounding effect of the projectile, in addition to its threshold velocity, weight and diameter, are:

  • Constructional Material– Lead is being replaced by mild steel, copper, etc.
  • Shape of Projectile– The better penetration of the projectile body is facilitated by a pointed nose of the projectile, which is present in all high-velocity projectiles. The ideal shape of the projectile for better penetration into the target is found to be stream-lined bullets.
  • Stability of Bullet– The ideal bullet with optimum wounding effect enters the body from the near nose onwards without getting fragmented or deformed. After entering into the body, it transfers the energy to inflict the injury. A hard projectile with a sufficient sectional density pierces the body( skin, flesh, and bone) without getting damaged.
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4. Range of Fire

In addition to reducing the threshold velocity of the projectile, the increasing range of firing influences the wounding effect in the following ways.

  • The gases and the lighter particles of the ejected projectile are dispersed. They do not reach the target.
  • The initial instability of the projectile goes away, and the bullet does not wobble except at extreme ranges.

Conclusion

The threshold velocity is the minimum velocity required by the projectile to penetrate the skin, flesh, or bone. The projectile’s wounding effects are also dependent on the factors such as the range of fire, constructional features of the projectiles, and the target site.

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