Injuries & Quantity of Energy of Projectile

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Injuries caused by bullet depends on multiple factors affecting the transmission of kinetic energy of projectile to the tissues. The extent of firearm injury is due to:

1.Mechanical crushing and shredding of tissues in the course of penetration of bullet in the body.

2.Compression,stretching and shearing of tissues caused by temporary cavity formation by the bullet in body.

3.Fragmentation of bullet in the body causing secondary injury

4.Length of bullet wound track.

5.Nature of tissue perforated by bullet.

Many people believe that a gunshot wound occurs when a bullet passes through a person like a drill bit through wood, boring a tidy hole through the structures it passes through while shredding and crushing tissue along the bullet’s path. This belief is incorrect. When a bullet passes through the body, it crushes and shreds the tissue in its route while propelling outward the surrounding tissue from the bullet’s path, creating a temporary cavity far wider than the bullet’s diameter. This temporary cavity, which lasts 5–10 milisecond from initial rapid expansion to final collapse, passes through a succession of minor pulsations and contractions before disappearinry caused by bulletg and leaving the permanent wound track.

The maximal diameter of this cavity is many times that of the bullet, albeit medical literature has exaggerated this. The greatest cavity diameter looks to be around 12.5 times the missile diameter, according to Fackler. The nature of the bullet, the amount of kinetic energy lost by the bullet on its route through the tissue, the rate at which the energy is lost, and the elasticity and cohesiveness of the tissue all influence the location, size, and form of the temporary cavity in the body.

Kinetic energy is present in a moving projectile because of its velocity. The weight and velocity of a bullet determine the energy it has:

The kinetic energy is equal to weight of projectile multiplied by square of its velocity,divided by 2 times acceleration due  gravity.

K.E.= WVsquare/2g

Where g is the gravitational acceleration, 

The bullet’s weight is W, and its speed is V.

The quantity of kinetic energy possessed by a bullet is determined more by its velocity than by its weight, as can be shown from this formula. The kinetic energy is doubled when the weight is doubled, but quadrupled when the velocity is doubled. The greater the temporary cavity in a given tissue, the more kinetic energy lost by a bullet.The temporary cavity phenomenon is relevant in the case of rifle bullets since it has the potential to be one of the most critical elements in determining an individual’s injury extent. However, in order for this potential to be realised, not only must a huge temporary space be established, but it must also develop in strategically crucial tissue, such as the liver. The organs that a bullet passes through have an impact on the severity of the wound.Stretch injury is less common in elastic tissues including the lungs, bowels, and muscles. The liver, for example, is not one of them.Stretch from the temporary cavity can disrupt blood vessels and fracture bone, however this is more theoretical than practical in the case of bone.The size of the temporary cavity is proportional to the amount of kinetic energy lost in the tissue, rather than the bullet’s total energy. When a bullet enters a body but does not depart, all of the kinetic energy is used to generate a wound. When a bullet perforates the body, however, only a portion of the kinetic energy is utilised to generate the wound. Because A perforates the body, whereas B does not, bullet A with double the kinetic energy of bullet B may create a less severe wound than bullet B.This presupposes that the bullets go in the same direction through the body.

A bullet’s kinetic energy loss is determined by four key elements.

1. The quantity of kinetic energy possessed by the bullet at the time of impact is the first consideration. This is determined by the bullet’s velocity and mass.

2. The angle of yaw of a bullet at the time of impact is the second component. A bullet’s yaw is defined as the departure of the bullet’s long axis from its line of flight. When a bullet is fired down a rifled barrel, the rifling causes the bullet to spin gyroscopically. The spin’s aim is to keep the bullet’s flight in the air stable.
As the bullet exits the barrel, it spins on its long axis, which corresponds to the flight path. However, as soon as the bullet leaves the barrel, it starts to wobble or yaw. The amount and degree of yaw of a bullet is determined by the bullet’s physical properties (length, diameter, and cross-sectional density), the barrel’s twist rate, and the density of the air. Only military weaponry have been able to identify yaw angles with precision. The angle of yaw tends to decrease as the bullet moves away from the gun, though there may be some variances. Temperature extremes can increase yaw and consequently the bullet’s stability.

The angle of yaw can be changed by changing the rate of twist in the barrel or the weight of the projectile. The greatest amplitude of the yaw (the degree of yaw) gradually diminishes as the bullet goes further away from the muzzle. The fact that close-up wounds are generally more devastating than distant wounds is due to the bullet’s stabilisation as the range increases. It also explains why a rifle bullet penetrates farther at 100 yards than it does at 10 feet. Although the bullet’s gyroscopic spin along its axis is adequate to keep it stable in air, it is insufficient to keep it stable when it reaches the denser medium of tissue, causing it to wobble and increase its yaw.

The bullet’s cross-sectional area grows greater as it wobbles, the drag force increases, and more kinetic energy is wasted. If the bullet’s route through the tissue is long enough, the yawing will increase to the point where it will rotate 180 degrees and move base forward. Shorter projectiles tend to tumble faster than longer ones. When a bullet yaws, it presents a substantially bigger cross-sectional area to the target. As a result, there is more direct tissue destruction, more kinetic energy loss, and a larger temporary cavity. The quick rise in drag force caused by yawing puts a lot of strain on the bullet, and it may break up.

One final aspect to consider regarding kinetic energy and the production of temporary cavities is that no matter how large a temporary cavity a bullet creates, it will have little or no effect unless it occurs in an organ susceptible to injury from such a cavity. A 3 in. cavity in the liver wounds more effectively than a similar cavity in the thigh muscle.

3. The bullet itself: its caliber, manufacturing, and configuration, is the third component that determines the amount of kinetic energy lost in the body. Because blunt-nose bullets are less streamlined than spitzer (pointed) bullets, they are slowed more by tissue and lose more kinetic energy. Expanding bullets are delayed more than streamlined full-metal-jacketed bullets, which resist expansion and lose just a small amount of kinetic energy as they pass through the body. The initial value of the area of interphase between the bullet and the tissue, and thus the drag of the bullet, are determined by the size and shape of the bullet, i.e., the bluntness of the nose. When a bullet deforms, its shape and caliber become less important. The degree of deformation, in turn, is determined by the bullet’s structure (the presence or lack of jacketing; the length, thickness, and hardness of the jacket material; the hardness of the lead utilized in the bullet; and the presence of a hollow point) as well as its velocity. When a bullet travels faster than 340 m/s enters tissue, it begins to distort. It is above 215 m/s for hollow points. Soft-point and hollow-point centrefire rifle bullets with lead cores not only expand but also shed lead bits as they pass through the body. Regardless of whether they hit bone or not, they shed. The lead fragments that fly off the main bullet mass operate as secondary missiles, touching more and more tissue and therefore increasing the size of the wound cavity and consequently the wound severity. Unless handgun bullets impact bone, this phenomenon, the shedding of lead pieces, does not occur to any considerable degree with soft point or hollow point bullets. The velocity of missiles appears to be connected to their breaking up. Even with the new high-velocity loadings, the velocity of handgun bullets is insufficient to induce the shedding of lead fragments seen with rifle bullets. Full-metal-jacketed rifle bullets can break up in the body without impacting bone, which is a fact that is often overlooked. The velocity and tendency to radically yaw of a full-metal-jacketed bullet determine its likelihood of breaking up in the body. When a bullet yaws a lot, its projected cross-sectional area expands dramatically, which increases the drag force pressing on the bullet. The quick rise in drag force puts a lot of strain on the bullet’s structure, which causes it to break up. All of this leads to a higher loss of kinetic energy as the wound becomes more severe. Callendar and French found that blunt-nosed bullets break up from the tip, whereas pointed bullets break up from the base, when discussing the tendency of high-velocity, full-metal-jacketed bullets to break up. If the bullet is subjected to high stress, such as tumbling, the lead core can be forced out of the base in both types of full-metal-jacketed bullets. Fackler et al. claim that all copper-jacketed rifle bullets with a lead core break when contacting tissue and causing tissue stimulation at speeds more than 900 m/s.
4. The density, strength, and elasticity of the tissue struck by a bullet, as well as the length of the wound track, are the fourth characteristics that determine the amount of kinetic energy lost by a bullet. The greater the retardation and kinetic energy loss, the denser the tissue through which the bullet passes. Increased density causes the yaw to increase and the gyration period to shorten. Because of the larger yaw angle and shorter gyration time, there is more retardation and kinetic energy loss.