Je vous partage un site qui, je trouve, développe bien sur le sujet:
www.ballisticstudies.comVoici un extrait à propos du "Game Killing Fundamentals -
Effective Game Killing" ou Principes fondamentaux pour tuer efficacement le gibier.
Bon ok, c'est en anglais mais c'est très bien développé.
(adresse:
http://www.ballisticstudies.com/Knowledgebase/Game+Killing+Fundamentals.html)Après une longue partie sur l'histoire de la balistique de chasse, l'article traite de ce qui suit:
How bullets kill
A projectile kills by causing either one or a combination of the following:
1. Blood loss
2. damage to the nervous system
3. destruction of vital tissue and organs
4. blood poisoning or asphyxiation
Each causing the effect that life can no longer be sustained.
For hunting purposes, the primary task of the projectile is to provide a fast humane kill. This minimizes suffering to the animal and simplifies location of the carcass. Destruction of the major nervous centers such as the brain or forwards portion of the spine cause the fastest killing but such targets are often difficult to hit.
The most reliable method of killing is through causing blood loss. Blood loss is categorized as either fast bleeding or slow bleeding. Fast bleeding refers to the destruction of the major arteries of the chest and neck creating a fast kill while slow bleeding refers to the muscles and arteries that feed them, such as the femoral artery. When slow bleeding areas are destroyed, the result is a slow kill.
When a projectile destroys vital organs such as the lungs, liver or heart, death occurs in the first instance through blood loss, not through the destruction of the organ itself. This is simply because these organs are major carriers of blood therefore kills are relatively fast.
Slow kills can also be caused by asphyxiation as a result of minor wounding to the lungs or neck while gut shots cause a slow death through blood poisoning by the introduction of digestive acids into the bloodstream .
The modern high power sporting cartridge relies on high velocity loaded with soft expanding type projectiles. As the projectile strikes flesh, it mushrooms (or tumbles) causing displacement of tissue through both physical contact as well as pressure. The projectile transfers its kinetic energy to the surrounding tissue causing acceleration of fluid particles in and around its path. This creates an explosive temporary wound channel that subsides to a wound channel far greater than the diameter of the projectile. The temporary wound channel reaches its maximum size within one millisecond, collapsing to its final size within several milliseconds. The size of the temporary wound channel is proportional to how much energy is delivered and can be given numerical values. In both military and sporting applications these two types of wound damage are referred to as the temporary wound channel and permanent wound channel, both having the effect of causing blood loss, organ and nerve damage relative to shot placement.
Fast Killing
Fast killing is an important factor for two reasons. The first is with regards to humane killing. Compassion must always be at the fore front of the hunters mind, at least in my opinion. The second factor of importance is the ability to secure game quickly, without losing the animal. In bush hunting situations it is not uncommon for a dead run animal to be lost after traveling between 100 and 300 yards before expiring, falling into a gut or hole, never to be seen again. Frustrating, isn’t it? For the tops hunter, it means securing an animal on the ledge it was perched on. Dead running game on the tops can very easily expire when traversing a ravine, the animal falling, becoming stuck in a position that is neither recoverable from the top or bottom of the bluff system. Been there, done that, don’t want to go through it again.
In order to get the best results, it is important to understand the mechanisms of killing and how a fast kill occurs.
A common misconception when witnessing game collapse at the moment the bullet impacts, is that the force of the projectile has physically knocked the animal to the ground. We tend to call this an instant kill. Newton’s law suggests that for every force there is an equal and opposite force. To this end, the force of the bullet impacting game is no greater than the recoil of the rifle. So what causes the instant collapse or poleaxe as it is often caused?
Instant collapse occurs when the central nervous system (CNS) is damaged or electrically disrupted as a result of one of two mechanisms, either direct or indirect contact.
With direct contact, a bullet directly striking and destroying one of the major nerve centers, including the thoracic and cervical vertebrae, the brain or the autonomous plexus, regardless of velocity, will result in instant death.
Indirect contact refers to the effects of a high velocity bullet imparting its energy, creating a hydrostatic shock wave. In terminal ballistics, the terms hydraulic shock and hydrostatic shock both refer to kinetic energy transferred as shock waves through flesh however, each term describes different results. Hydraulic shock is a civil engineers term also known as water hammer but in terminal ballistics context refers to the pressure of accelerated fluid particles that create the temporary wound channel. Hydrostatic shock transfer refers to the effect when shock waves travel through flesh to distant nerve centers, disrupting their ability to emit electrical impulses.
The reason why game animals drop instantly with chest shots that do not directly strike the CNS, is due to hydrostatic shock transfer to the spine and brain. A high velocity cartridge well matched to game body weights imparts over half its energy within the first 2cm of penetration, creating a shock wave. This shock wave travels outwards via the rib cage until it reaches the spine where it disrupts the electrical impulses of the CNS. The result to the animal is an immediate loss of consciousness.
Along with the loss of consciousness, the projectile has also created a large wound channel, draining all of the body’s blood within several seconds. The loss of blood and damage to vital organs cause death to the animal before it has the chance to regain consciousness. This action creates the illusion to the hunter, that the projectile has knocked its victim to the ground, killing it instantly. More careful examination shows that the shot caused coma, followed by blood loss, followed by death. The hydrostatic shock created by a hunting bullet is identical in action to when a boxer is struck on the jaw by his opponent, disrupting the functions of the brain with a resulting loss of consciousness.
Hornady testing has revealed that a large wound cavity can cause a blood pressure spike to the brain, inducing immediate coma, though this is relative to hydraulic shock, not hydrostatic shock as described here. This phenomena also helps produce ethical killing.
Four major factors affect whether hydrostatic shock transfer occur and all are relative to each other.
1. Velocity. This has the greatest effect on hydrostatic shock. Put simply, the higher the impact velocity, the greater the shock. Velocity is also the most influencing factor in hydraulic shock, having a huge bearing on the size of the internal wound channel. Hydrostatic shock, in bore sizes from .243” up to .338”, begin to lesson at impact velocities below 2600fps and most modern high velocity sporting cartridges including the magnums gradually lose shocking power beyond 300 to 350 yards. Of the thousands of animals harvested during TBR tests, 2600fps has been the most common cut off point with repeatable results (reactions) occurring when deliberately testing the impact velocity of 2650fps versus the impact velocity of 2550fps.
A noticeable change occurs as bullet diameter is increased to .358” (such as the .35 Whelen) and larger bores. With the medium and large bores, hydrostatic shock can occur on our NZ game species at velocities as low as 2200fps.
Frangible bullets tend to produce coma at much lower velocities than traditional hunting bullets. With frangible bullets at low velocities, instant coma is due to hydraulic shock causing blood pressure spikes in the brain as discovered by Hornady ballisticians. These results can easily be seen in the field. In other instances, coma follows shortly after impact, most likely due to multiple pain centers being disrupted to such an extent that the animal must go into coma.
When testing hydrostatic shock on Bovines, it was discovered that impact velocities of 2600fps with suitable bullet weights (and construction) produced instant poleaxe in a repeatable manner. However, in many instances, Bovines would attempt to rise but that the action of attempting to rise resulted in increased blood loss with death following within seconds.
2. Bullet weight versus game weights. Where the bullet is too light for the intended game it may simply lack enough kinetic energy to cause hydrostatic shock, meeting far too much resistance on impact. This is a common occurrence with the .22 centrefires but can also occur in any cartridge, especially the large magnums when using light, very soft projectiles. A good example of this can be found in the 7mm Remington magnum loaded with various 140 grain fast expanding bullets. Although internal wounding may be sufficient, without hydrostatic shock, game break into a dead run.
Less obvious, is the result of using a bullet weight that is too heavy for the intended game. If the projectile contains too much momentum, the bullet may fail to meet enough resistance to impart energy where it is required i.e. the ribs through to the spine. Wound channels may be as wide as a lighter bullet however; the hunter may find that game run a long way before succumbing to the shot. These factors can create many difficulties for the hunter when selecting an appropriate load as a certain level of momentum is required if the bullet is expected to penetrate into vitals from any angle or give satisfactory performance on a variety of game.
A good example of a projectile that can cleave to its momentum is the Barnes homogenous copper bullet. Looking at the .308 Winchester, the 150 grain TSX, while being a very effective projectile for large bodied deer, can cause slow kills on light bodied deer at ranges beyond 75 yards (impact velocity of 2600fps and below). Internal wounding may well be very thorough, yet game still run considerable distances. In contrast, the lighter 130 grain TSX (along with the 130 grain GS Custom bullets) not only utilize higher impact velocities, but also meet greater resistance on impact, initiating more traumatic wounding.
3. Projectile construction. The third factor that effects hydrostatic shock transfer and counteracts bullet weight while also having the capacity to counteract impact velocity is bullet construction. For example, the stout Sierra .30 caliber 180 grain Prohunter, whether driven from the .308 Winchester or .300 Win Mag creates a large internal wound on goat fallow and Sika, yet it can retain too much momentum to initiate hydrostatic shock on these animals and kills can be very slow. The same can be said of some of the stout core bonded designs such as the 180 grain InterBond along with the Barnes TXS bullets. By simply changing to the 180 grain Speer BTSP or 178 grain A-Max, a faster kill can be obtained. These two projectiles are soft and highly frangible. The Hornady A-Max in particular can produce hydrostatic shock at impact velocities of 2000fps or lower where the ProHunter shows a clear cut off point at an impact velocity of 2550fps.
In contrast, as game body weights reach 90kg and above, the 180 grain Prohunter and its GameKing sibling along with the InterBond and TSX bullets, all come into their own, meeting a great deal of resistance on impact. Hydrostatic shock is still absent at impact velocities of 2600fps and below, but the heavy resistance initiates immense trauma and broader internal wounding than on lighter game body weights, resulting in a kill that is delayed by only a few seconds, as opposed to up to 45 seconds.
4. The fourth factor is bullet diameter.
Pour ma part, j'ai appris à propos du wound tunnel, du hydrostatic shock vs hydraulic shock.
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Mer 19 Nov 2014 - 21:57
