Effective Game Killing – Part 1
By Nathan Foster
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. Septicemia 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. Gut shots cause a slow death through infection (septicemia) along with the introduction of digestive acids into the bloodstream and any surrounding damaged organs. A commonly used term for death from gut shots is 'blood poisoning' which although gives little away in its description, does at least partially indicate that gut shots do not produce an immediate kills. Put simply, a gut shot can cause immense suffering.
Mechanisms
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.
At this point I would urge readers to ditch the temporary versus permanent wound channel terminology. Such terms may make us sound like experts in the know of such things but help us little in the field. A hunter does not walk up to a kill and state, "boy, you should have seen that temporary wound channel, lucky I didn't blink". I do not believe any human has the ability to see such things frame by frame and therefore, a wise man should drop such intellectual pontification. There are far more important factors to focus on…
Fast Killing
To begin with, please understand that much of the information presented from here is unique to my own research. You will not read the same in other places unless the information has been derived from my research. Although there are many people who work as experts in the field of terminal ballistics, I firmly believe that there is still a great level of misunderstanding within this subject.
Fast killing is an important factor for two reasons. The first is with regards to humane killing. Compassion must always be at the forefront 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 collapses 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.
Direct contact refers to a bullet directly striking and destroying one of the major nerve centers, including the thoracic and cervical vertebrae, the brain or the autonomic plexus, regardless of velocity, this 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 the civil engineer's 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.
Be very much aware that the terms hydraulic and hydrostatic shock are quite often misused by both hunters and professionals - including ballisticians working for bullet making companies.
Wide, disproportionate to caliber wounding (hydraulic shock) thanks to the 162gr Hornady SST combined with high velocity which also caused hydrostatic shock (instant collapse).
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 which passes through to the 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 electrical shock wave travels outwards via the rib cage until it reaches the spine and then continues through to the brain (CNS). The result is an immediate loss of consciousness as the body shuts down for diagnostics.
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 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.
The Stasborg tests also 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 phenomenon also helps produce ethical killing.
Four major factors affect whether hydrostatic shock transfer occur and all are relative to each other.
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", begins to lessen 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.
High velocity is not however a sole factor to be worshipped and held above other factors. For example, if velocity is increased too far without increasing bullet weight, the surface tension of water within the animal can cause so much resistance as to overcome the energy of the bullet. Ultra-high velocities can then also lead to shallow penetration. Generally speaking, the high velocity cut off point for small bore bullets used on medium game is around 3150fps. If for example we are using a 140 grain 7mm bullet at an impact velocity of 3250fps, chances are that even if the bullet penetrates vitals, the animal may still run some distance.
One factor to be very careful of with ultra-high velocity conditions is to not blame a delayed kill exclusively on 'bullet blow up'. For example, if we were using the same 140gr 7mm bullet and the entry wound did indeed show signs of wide entry wounding and surface bullet blow up (or possibly blow back), even though this is undesirable performance, we still need to investigate further if we are to truly understand factors at play. In this instance, once the animal is recovered, it is important to study the vital organs and determine whether they were actually destroyed. If the vitals were destroyed, we can then conclude that the bullet did its job (even if in a less than desirable manner) but without hydrostatic shock.
A noticeable change in hydrostatic shock occurs as bullet diameter is increased to .358" (such as the .35 Whelen) and larger bores (see bullet diameter). With the medium and large bores, hydrostatic shock can occur on our medium game species at velocities as low as 2200fps. Fast incapacitation can remain evident at velocities as low as 1800fps depending on bullet designs. Below 1800fps, the wider the bore the better. Further to this, there are also highly traumatic pistol bullet designs such as the Hornady XTP.
Frangible bullets tend to produce coma at much lower velocities than traditional hunting bullets (see bullet construction). With frangible bullets at low velocities, instant coma may be due to hydraulic shock causing blood pressure spikes in the brain as suggested by Hornady ballisticians. In other instances, coma can follow very shortly after impact due to multiple pain centers being disrupted to such an extent that the animal must go into coma. That said, frangible bullets may also send out particles which strike the CNS directly.
When testing hydrostatic shock on Bovines, I have 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, the action of attempting to rise resulting in increased blood loss with death following within seconds.
Bullet weight versus game weights
If 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 a common occurrence with the .22 centrefires but can also occur in any small bore cartridge especially the large magnums when using soft, light for caliber projectiles. If the bullet is driven too fast and lacks sufficient weight, it can also fail to initiate hydrostatic shock (see Velocity).
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 cartridge and bullet 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 body weights.
Quite often a .30 caliber 180 grain hunting style bullet is simply too stout and carries too much momentum to initiate hydrostatic shock / rapid coma on lean bodied deer - even at magnum velocities. The bullet may produce a nice mushroom and seemingly adequate internal wounding; however game may run a long way before expiring. A simple change to a 150 or 165 grain bullet can make all the difference in these instances. That or a change in bullet construction such as changing from a core bonded bullet to a fast expanding design like the Hornady SST. Energy retention as a result of heavy bullet construction and the retention of momentum can be even more of a problem in the .338 bore which has many projectiles designed specifically for Elk hunting. Furthermore, many hunters use match bullets in the .338 for long range hunting, some of which are simply hopeless on game.
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 Pro-Hunter, whether driven from the .308 Winchester or .300 Win Mag creates a large internal wound on light or lean bodied deer, 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, the 180 grain SST or 178 grain A-Max, a faster kill can be obtained. These projectiles are soft and frangible. The Hornady A-Max in particular can produce fast coma 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 (200lb) and above, stout bullets begin to come into their own, meeting a great deal of resistance on impact. Hydrostatic shock is still absent at impact velocities below 2600fps, however the heavy resistance of larger bodied medium game helps initiate 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.
The further you shoot, the softer your bullet needs to be in order to affect a wide wound and fast killing at low velocities. This is discussed at length within my long range hunting book series. At closer ranges, a tougher bullet may be needed in order to ensure adequate penetration. There may also be times when you need to dual load which is again discussed within the book series but also within the knowledge base. An example of dual loading might be as an example, having a 140 grain Nosler Partition in the top of the magazine of your 6.5x55 rifle while under this, you have three or four 143 grain ELD-X bullets ready for long range work.
Perhaps the greatest challenge hunters now face when choosing bullets, are the challenges presented by homogenous copper bullet designs. These are the toughest bullets on the market and due to their design, are unable to shed weight and lose momentum for maximum energy transfer. Some designs boast petal loss as a means to aid energy transfer but such features can make the bullet even worse, causing the shank of the remaining bullet to pencil through game creating narrow wounding, especially at lower impact velocities.
Homogenous bullets work best at high impact velocities. The bullet makers know well that momentum is a problem and in more recent years have generally worked towards offering lighter and then lighter still bullet designs. This reduction in weight and bullet length greatly aids wounding so long as velocity can be kept high. Homogenous copper bullets tend to initiate hydrostatic shock like other bullet designs at impact velocities above 2600fps providing the bullet weight is properly matched to game weights. In the .30 caliber, this can mean dropping right back to a 130 or even a 110 grain bullet design. Wounding generally remains adequate to 2400fps. Below 2200fps, all bets are off, especially if shot placement is less than ideal. Game may run long distances and may not allow the hunter the opportunity for a follow up shot.
The greatest benefit of homogenous copper bullets is that they penetrate well. The Barnes TSX for example, creates both excellent wounding and penetration when properly matched to game weights and used in high velocity cartridges out to moderate ranges. This is a homogenous copper bullet at its best, tackling tough animals from varying angles. But to say that one can eat up to the bullet hole (in the absence of lead toxicity) can be rather misleading. The current Tipped TSX design (used in high powered cartridges) can cause gut ruptures as a result of hydraulic forces, spreading gut material into meat. Those concerned about meat damage or meat fouling need to understand this - bullets kill via destruction of tissue. We can't always have it both ways.
Unfortunately in the rush to market their bullets as environmentally friendly, governments have lapped up these bullet designs and there are now states and countries which have banned the use of lead bullets for hunting. The downside of this is that many animals have and will die slowly as a result of a combination of the design of these bullets and their misuse.
Homogenous copper bullets need to be driven fast, bullet weights needs to be selected with care while shot placement needs to be taken into due consideration. Please do not buy into these bullets as being 'the only choice for the future' as greedy corporates and their green government friends might have you believe. There are other ways we can move ahead. We can have our cake and eat it too with the likes of the DRT bullet design. This bullet has a copper jacket and compressed powdered metal core and works much like many of the traditional bullets currently available. Having said this, DRT are but one company carrying the spark of a possible future and at this time of writing have limited options. Nevertheless, I urge readers to investigate what DRT have to offer.
Bullet diameter
The fourth factor is bullet diameter and put simply, the wider the caliber, the less need there is for high velocity to initiate shock. Bullet weight can be high (200-300 grains) yet kills may be faster than our stout .30 caliber 180 grain bullet example from earlier. This can be due to the wider frontal area meeting more resistance on impact, or a reduction in momentum (the bullet may be short even though it is heavy due to its width) or a combination of both. The net result is that a medium or large bore can break all the rules we are familiar with when using small bores and with or without high velocity, produce very fast killing.
As previously mentioned, small bores generally behave in a similar manner with regards to hydrostatic shock cut off point. But a major change is seen once we step up to the .358 bore which can produce hydrostatic shock on medium game at velocities of 2200fps and lower.
On heavy game and using a medium or large bore with heavy (e.g. 300 grains plus) and sturdy projectiles, it is possible to initiate hydrostatic shock at impact velocities above 2600fps. However, this is more of a factor of bullet weight and velocity as opposed to being strictly related to bullet diameter.
Unfortunately, having a wide bullet cannot in itself fully compensate for or overcome any issues as a result of bullet construction. If the jacket of the medium or large bore bullet has been designed for heavy game, chances are that kills on light or lean game may be delayed, though internal wounding may be wide directly as a result of hydraulic forces. But if on the other hand the bullet has been designed for general hunting such as is found throughout the .358 bore, one can expect generally fast 'knockdown' (often exceptional performance) on a wide range of game. A key factor here is to understand that even if you opt for a medium or big bore as 'the fix' to quickly anchor game in difficult to track bush / woods / swamp, you will still have to match bullet construction to the job at hand. If you choose a very stout and heavy bullet and use this on a lean bodied deer, the animal may still run.
The shape of the bullet tip also effects performance. Match bullets (without a plastic tip) tend to have very small hollow points which can at times lead to a failure to expand and therefore narrow wounding. Plastic tip bullets often disguise a very wide hollow point behind their tip. Hollow point hunting bullets can also offer a wide frontal area, simply lacking the plastic disguise. This subject also crosses over to bullet construction. For example, a wide hollow point will generally be weaker at the tip so it has both width and weakness to aid in energy transfer.
Lead soft point bullets can differ vastly in performance from one design to the next. Some are pointed, others round nose while some are flat tipped.
Interestingly, the differences in terminal performance between round or flat nosed bullets and pointed bullets tend to become more pronounced as we increase bore and bullet diameter. For example, the .358 Hornady 250 grain spire point can produce delayed kills on medium game while its 250 grain round nosed counterpart can produce very fast coma. The same can be said of the medium bore Woodleigh Weldcore bullets. Obviously, the faster a bullet dumps its energy, the sooner it will run out of energy for penetration which may or may not be a good thing depending on the size animals we are hunting.
Nathan Foster has a long established background in the gun industry, recognized for his extensive research and for educating and supporting hunters around the world. Nathan has taken over 7500 head of game, testing the performance of a wide range of cartridges and projectiles, and is a worldwide expert in the field of terminal ballistics. His ongoing research has been carefully recorded, analyzed and documented in his online cartridge knowledge base for the benefit of all hunters and shooters (www.ballisticstudies.com). Rifle accurizing and long range shooting are among Nathan's specialties. For many years, Nathan has provided both rifle accurizing services and a long range shooting school. Nathan is also the designer of MatchGrade bedding products and has assisted many 1000's of hunters worldwide to improve their rifle accuracy, shooting technique and hunting success.
Nathan Foster'sThe Practical Guide to Long Range Hunting Cartridges guides you through the process of choosing a cartridge and a projectile which suits you and your goals - step by step. This book, like many of Nathan's books and writings, takes the approach that there is no need for you to be told which is the best cartridge for you - you can answer that question for yourself once you know how.
Instead the reader is taught the fundamental principles of long range game killing and is then given a methodical process for selecting the right cartridge based on their goals. The book looks at the various individual cartridge designs and the advantages and disadvantages of each cartridge so that the reader can then align their needs with an appropriate cartridge and projectile to get the job done.
By Nathan Foster
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. Septicemia 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. Gut shots cause a slow death through infection (septicemia) along with the introduction of digestive acids into the bloodstream and any surrounding damaged organs. A commonly used term for death from gut shots is 'blood poisoning' which although gives little away in its description, does at least partially indicate that gut shots do not produce an immediate kills. Put simply, a gut shot can cause immense suffering.
Mechanisms
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.
At this point I would urge readers to ditch the temporary versus permanent wound channel terminology. Such terms may make us sound like experts in the know of such things but help us little in the field. A hunter does not walk up to a kill and state, "boy, you should have seen that temporary wound channel, lucky I didn't blink". I do not believe any human has the ability to see such things frame by frame and therefore, a wise man should drop such intellectual pontification. There are far more important factors to focus on…
Fast Killing
To begin with, please understand that much of the information presented from here is unique to my own research. You will not read the same in other places unless the information has been derived from my research. Although there are many people who work as experts in the field of terminal ballistics, I firmly believe that there is still a great level of misunderstanding within this subject.
Fast killing is an important factor for two reasons. The first is with regards to humane killing. Compassion must always be at the forefront 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 collapses 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.
Direct contact refers to a bullet directly striking and destroying one of the major nerve centers, including the thoracic and cervical vertebrae, the brain or the autonomic plexus, regardless of velocity, this 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 the civil engineer's 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.
Be very much aware that the terms hydraulic and hydrostatic shock are quite often misused by both hunters and professionals - including ballisticians working for bullet making companies.
Wide, disproportionate to caliber wounding (hydraulic shock) thanks to the 162gr Hornady SST combined with high velocity which also caused hydrostatic shock (instant collapse).
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 which passes through to the 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 electrical shock wave travels outwards via the rib cage until it reaches the spine and then continues through to the brain (CNS). The result is an immediate loss of consciousness as the body shuts down for diagnostics.
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 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.
The Stasborg tests also 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 phenomenon also helps produce ethical killing.
Four major factors affect whether hydrostatic shock transfer occur and all are relative to each other.
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", begins to lessen 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.
High velocity is not however a sole factor to be worshipped and held above other factors. For example, if velocity is increased too far without increasing bullet weight, the surface tension of water within the animal can cause so much resistance as to overcome the energy of the bullet. Ultra-high velocities can then also lead to shallow penetration. Generally speaking, the high velocity cut off point for small bore bullets used on medium game is around 3150fps. If for example we are using a 140 grain 7mm bullet at an impact velocity of 3250fps, chances are that even if the bullet penetrates vitals, the animal may still run some distance.
One factor to be very careful of with ultra-high velocity conditions is to not blame a delayed kill exclusively on 'bullet blow up'. For example, if we were using the same 140gr 7mm bullet and the entry wound did indeed show signs of wide entry wounding and surface bullet blow up (or possibly blow back), even though this is undesirable performance, we still need to investigate further if we are to truly understand factors at play. In this instance, once the animal is recovered, it is important to study the vital organs and determine whether they were actually destroyed. If the vitals were destroyed, we can then conclude that the bullet did its job (even if in a less than desirable manner) but without hydrostatic shock.
A noticeable change in hydrostatic shock occurs as bullet diameter is increased to .358" (such as the .35 Whelen) and larger bores (see bullet diameter). With the medium and large bores, hydrostatic shock can occur on our medium game species at velocities as low as 2200fps. Fast incapacitation can remain evident at velocities as low as 1800fps depending on bullet designs. Below 1800fps, the wider the bore the better. Further to this, there are also highly traumatic pistol bullet designs such as the Hornady XTP.
Frangible bullets tend to produce coma at much lower velocities than traditional hunting bullets (see bullet construction). With frangible bullets at low velocities, instant coma may be due to hydraulic shock causing blood pressure spikes in the brain as suggested by Hornady ballisticians. In other instances, coma can follow very shortly after impact due to multiple pain centers being disrupted to such an extent that the animal must go into coma. That said, frangible bullets may also send out particles which strike the CNS directly.
When testing hydrostatic shock on Bovines, I have 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, the action of attempting to rise resulting in increased blood loss with death following within seconds.
Bullet weight versus game weights
If 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 a common occurrence with the .22 centrefires but can also occur in any small bore cartridge especially the large magnums when using soft, light for caliber projectiles. If the bullet is driven too fast and lacks sufficient weight, it can also fail to initiate hydrostatic shock (see Velocity).
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 cartridge and bullet 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 body weights.
Quite often a .30 caliber 180 grain hunting style bullet is simply too stout and carries too much momentum to initiate hydrostatic shock / rapid coma on lean bodied deer - even at magnum velocities. The bullet may produce a nice mushroom and seemingly adequate internal wounding; however game may run a long way before expiring. A simple change to a 150 or 165 grain bullet can make all the difference in these instances. That or a change in bullet construction such as changing from a core bonded bullet to a fast expanding design like the Hornady SST. Energy retention as a result of heavy bullet construction and the retention of momentum can be even more of a problem in the .338 bore which has many projectiles designed specifically for Elk hunting. Furthermore, many hunters use match bullets in the .338 for long range hunting, some of which are simply hopeless on game.
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 Pro-Hunter, whether driven from the .308 Winchester or .300 Win Mag creates a large internal wound on light or lean bodied deer, 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, the 180 grain SST or 178 grain A-Max, a faster kill can be obtained. These projectiles are soft and frangible. The Hornady A-Max in particular can produce fast coma 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 (200lb) and above, stout bullets begin to come into their own, meeting a great deal of resistance on impact. Hydrostatic shock is still absent at impact velocities below 2600fps, however the heavy resistance of larger bodied medium game helps initiate 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.
The further you shoot, the softer your bullet needs to be in order to affect a wide wound and fast killing at low velocities. This is discussed at length within my long range hunting book series. At closer ranges, a tougher bullet may be needed in order to ensure adequate penetration. There may also be times when you need to dual load which is again discussed within the book series but also within the knowledge base. An example of dual loading might be as an example, having a 140 grain Nosler Partition in the top of the magazine of your 6.5x55 rifle while under this, you have three or four 143 grain ELD-X bullets ready for long range work.
Perhaps the greatest challenge hunters now face when choosing bullets, are the challenges presented by homogenous copper bullet designs. These are the toughest bullets on the market and due to their design, are unable to shed weight and lose momentum for maximum energy transfer. Some designs boast petal loss as a means to aid energy transfer but such features can make the bullet even worse, causing the shank of the remaining bullet to pencil through game creating narrow wounding, especially at lower impact velocities.
Homogenous bullets work best at high impact velocities. The bullet makers know well that momentum is a problem and in more recent years have generally worked towards offering lighter and then lighter still bullet designs. This reduction in weight and bullet length greatly aids wounding so long as velocity can be kept high. Homogenous copper bullets tend to initiate hydrostatic shock like other bullet designs at impact velocities above 2600fps providing the bullet weight is properly matched to game weights. In the .30 caliber, this can mean dropping right back to a 130 or even a 110 grain bullet design. Wounding generally remains adequate to 2400fps. Below 2200fps, all bets are off, especially if shot placement is less than ideal. Game may run long distances and may not allow the hunter the opportunity for a follow up shot.
The greatest benefit of homogenous copper bullets is that they penetrate well. The Barnes TSX for example, creates both excellent wounding and penetration when properly matched to game weights and used in high velocity cartridges out to moderate ranges. This is a homogenous copper bullet at its best, tackling tough animals from varying angles. But to say that one can eat up to the bullet hole (in the absence of lead toxicity) can be rather misleading. The current Tipped TSX design (used in high powered cartridges) can cause gut ruptures as a result of hydraulic forces, spreading gut material into meat. Those concerned about meat damage or meat fouling need to understand this - bullets kill via destruction of tissue. We can't always have it both ways.
Unfortunately in the rush to market their bullets as environmentally friendly, governments have lapped up these bullet designs and there are now states and countries which have banned the use of lead bullets for hunting. The downside of this is that many animals have and will die slowly as a result of a combination of the design of these bullets and their misuse.
Homogenous copper bullets need to be driven fast, bullet weights needs to be selected with care while shot placement needs to be taken into due consideration. Please do not buy into these bullets as being 'the only choice for the future' as greedy corporates and their green government friends might have you believe. There are other ways we can move ahead. We can have our cake and eat it too with the likes of the DRT bullet design. This bullet has a copper jacket and compressed powdered metal core and works much like many of the traditional bullets currently available. Having said this, DRT are but one company carrying the spark of a possible future and at this time of writing have limited options. Nevertheless, I urge readers to investigate what DRT have to offer.
Bullet diameter
The fourth factor is bullet diameter and put simply, the wider the caliber, the less need there is for high velocity to initiate shock. Bullet weight can be high (200-300 grains) yet kills may be faster than our stout .30 caliber 180 grain bullet example from earlier. This can be due to the wider frontal area meeting more resistance on impact, or a reduction in momentum (the bullet may be short even though it is heavy due to its width) or a combination of both. The net result is that a medium or large bore can break all the rules we are familiar with when using small bores and with or without high velocity, produce very fast killing.
As previously mentioned, small bores generally behave in a similar manner with regards to hydrostatic shock cut off point. But a major change is seen once we step up to the .358 bore which can produce hydrostatic shock on medium game at velocities of 2200fps and lower.
On heavy game and using a medium or large bore with heavy (e.g. 300 grains plus) and sturdy projectiles, it is possible to initiate hydrostatic shock at impact velocities above 2600fps. However, this is more of a factor of bullet weight and velocity as opposed to being strictly related to bullet diameter.
Unfortunately, having a wide bullet cannot in itself fully compensate for or overcome any issues as a result of bullet construction. If the jacket of the medium or large bore bullet has been designed for heavy game, chances are that kills on light or lean game may be delayed, though internal wounding may be wide directly as a result of hydraulic forces. But if on the other hand the bullet has been designed for general hunting such as is found throughout the .358 bore, one can expect generally fast 'knockdown' (often exceptional performance) on a wide range of game. A key factor here is to understand that even if you opt for a medium or big bore as 'the fix' to quickly anchor game in difficult to track bush / woods / swamp, you will still have to match bullet construction to the job at hand. If you choose a very stout and heavy bullet and use this on a lean bodied deer, the animal may still run.
The shape of the bullet tip also effects performance. Match bullets (without a plastic tip) tend to have very small hollow points which can at times lead to a failure to expand and therefore narrow wounding. Plastic tip bullets often disguise a very wide hollow point behind their tip. Hollow point hunting bullets can also offer a wide frontal area, simply lacking the plastic disguise. This subject also crosses over to bullet construction. For example, a wide hollow point will generally be weaker at the tip so it has both width and weakness to aid in energy transfer.
Lead soft point bullets can differ vastly in performance from one design to the next. Some are pointed, others round nose while some are flat tipped.
Interestingly, the differences in terminal performance between round or flat nosed bullets and pointed bullets tend to become more pronounced as we increase bore and bullet diameter. For example, the .358 Hornady 250 grain spire point can produce delayed kills on medium game while its 250 grain round nosed counterpart can produce very fast coma. The same can be said of the medium bore Woodleigh Weldcore bullets. Obviously, the faster a bullet dumps its energy, the sooner it will run out of energy for penetration which may or may not be a good thing depending on the size animals we are hunting.
Nathan Foster has a long established background in the gun industry, recognized for his extensive research and for educating and supporting hunters around the world. Nathan has taken over 7500 head of game, testing the performance of a wide range of cartridges and projectiles, and is a worldwide expert in the field of terminal ballistics. His ongoing research has been carefully recorded, analyzed and documented in his online cartridge knowledge base for the benefit of all hunters and shooters (www.ballisticstudies.com). Rifle accurizing and long range shooting are among Nathan's specialties. For many years, Nathan has provided both rifle accurizing services and a long range shooting school. Nathan is also the designer of MatchGrade bedding products and has assisted many 1000's of hunters worldwide to improve their rifle accuracy, shooting technique and hunting success.
Nathan Foster'sThe Practical Guide to Long Range Hunting Cartridges guides you through the process of choosing a cartridge and a projectile which suits you and your goals - step by step. This book, like many of Nathan's books and writings, takes the approach that there is no need for you to be told which is the best cartridge for you - you can answer that question for yourself once you know how.
Instead the reader is taught the fundamental principles of long range game killing and is then given a methodical process for selecting the right cartridge based on their goals. The book looks at the various individual cartridge designs and the advantages and disadvantages of each cartridge so that the reader can then align their needs with an appropriate cartridge and projectile to get the job done.
