Rifle Ballistics & Terminal Ballistics

[SteveP]

I've started this thread as a place to discuss terminal ballistics or what happens to an animal after it is shot in real life. This is somewhat relevant to The Alpha Wishlist discussions on hunting and shooting bears especially.

Some have expressed that a bear can be killed by a single .303 shot. While this is true to a degree, it is extremely dependent upon shot placement. A bear has a big heavy skull so a kill shot to the brain has an extremely small target area. A shot to the heart and lungs is preferred and an arterial shot to this area or any major artery should result in rapid bleed out and death within a few minutes.

Terminal Ballistics Hornady discussion of terminal ballistics

Terminal ballistics is the study of how a projectile behaves when it hits its target and transfers its kinetic energy to the target. The bullet’s design, as well as its impact velocity, plays a huge role in how the energy is transferred.

Also known as wound ballistics, terminal ballistics is important to hunters because it illustrates how a particular bullet will transfer its potiental energy when it strikes the target. Ethical hunters want as quick and humane a kill as possible, and death is ultimately caused in one of two ways:

• Severely interrupting or stopping the flow of oxygenated blood to the brain by damaging a major blood-bearing organ or by causing significant damage to the vascular system; or
  
• Causing severe damage to the brain and/or cerebellum.

Bullet design plays a very siginificant role in what kind of wound cavity the bullet will make in soft tissue. The type of wound cavity is critical to the quick and humane kill that hunters owe to the animals they hunt.

[SteveP]

Several comments have been made concerning the effective range of a particular rifle caliber and load. Bullet design and weight has a big effect upon this; if you are interested in the subject, I am most happy to provide additional material on the subject.

Essentially hunting for big game such as deer or bears typically involves ranged shots between 50 and 300 meters. A good hunting rifle such as a .303 typically has adequate power to make an effective shot group of about 6-10 cm (3-5 in) at up to 200 meters (or yards if you prefer) Snipers and expert marksmen can achieve even tighter groups of from 2-3 inch groups at that range. Therefore in the field you should only expect to be able to hit a bear or deer in the kill zone at most out to 300 meters. Field conditions also adversely affect the marksman's ability to make tight, accurate shots. Here is a relevant discussion: Mk4 #2 Enfield 303. Tactical project

The British .303 was designed with sights that ranged out to 800 yards so one could shoot at that range and still have enough stopping power (terminal energy) to seriously wound or kill (terminal energy is another complex calculation involving ballistics coefficient, bullet shape and weight, muzzle velocity, temperature and humidity and elevation) The chances of hitting your target at that range are extremely slim but you could lob shots (suppressing fire) to that range. So while you might be able to have a bullet fly perhaps 2 km or more, it is no longer considered effective at that range, just dangerous.

So by effective range, I mean the maximum distance you can accurately hit the target area and the stopping power of the bullet at that range.

We also discussed elsewhere the typically hunting ranges which are highly dependent upon the quarry and the type of country. You will find it difficult to get within 300 meters of a big horn sheep for example but you really want to get as close as 200 meters to have a much better chance of a good hit.

I suggest that if one were to seek realism in TLD, most of the shots taken in our territory would be between 200-300 meters or less given the open sights of the .303 in the game. Of course, in the game, there are places where one can find cover and have a nice easy shot of 20 meters; the same would be true in real hunting if one had a blind with cover or a tree blind and the wind is favorable. Hunters sometimes use scent to cover the human scent such as made from feces, dirt, mud and boiling other detritus. Needless to say, you can't get close if the animal can smell you! Bears especially rely upon their sense of smell which can detect blood for thousands of meters.

[SteveP]

There is another phenomenon of high powered rifle shooting called Hydrostatic shock and also Hydraulic Shock. This is where a high powered round enters the animal and fragments or mushrooms and delivers a huge shock to the target that severely destroys a lot of tissue and causes severe damage and bleeding. A shot to an upper area of a limb where there are major arteries can be lethal using that kind of shot, typically only available with a magnum load such as from a .308 magnum or a .344 magnum or higher. Bullet design is also critical.

Here is an excellent discussion of hydraulic and hydrostatic shock and other conditions affecting killing power.

Effective Game Killing

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.