Ballistics is an inexact science at best, and some theories which hunters and shooters think are carved in stone, aren’t really all that practical. These days more emphasis is being placed on bullets with higher ballistic coefficients, while sectional density doesn’t get much of a mention and hardly anyone seems to consider momentum. The efficient killing of deer-size animals is largely dependent upon three factors – striking energy which relies upon retained velocity, and bullet performance which is influenced by both energy and momentum.
Design of a bullet
Today’s premium hunting bullets offer controlled expansion over a wide range of impact velocities which naturally grow slower as the distance increases. Although accuracy and killing power have no surface relationship, the hunter soon becomes aware that a 100gn bullet placed in the animal’s heart, lungs,brain or spine is going to be more effective than a 400gn bullet that lands in the guts or the left hind foot. Even a tyro quickly learns that where the bullet strikes is more important than what bullet or loading he used. Varmint rifles and elephant rifles are equally deadly when their bullet pierces the game’s heart, and each is equally ineffective when its bullet succeeds only in breaking a leg.
The only manner in which game can be quickly killed is by the destruction of organs immediately essential to life or by the destruction of such a large amount of tissue that life can no longer be sustained. The latter result is effected when a bullet expands violently and creates a large wound channel. Usually, the larger the mushroom, the higher the degree of wounding.
Velocity is important
Even the best designed big-game bullet needs the help of velocity to provide a quick kill. Traditional soft-pointed lead- core bullets that mushroom will penetrate deeply only after their initial high velocity has dropped off, but if properly placed would certainly inflict a fatal wound. The latter result is effected when quite powerful rifles are used on animals which are relatively small in relation to the energy of the bullet. This method seems to require about 100 foot-pounds of bullet energy for each live-weight pound of animal.
To score an instant kill with the usual deer rifle, exact bullet placement is required in a vulnerable area. The required degree of bullet placement will vary almost directly in proportion to the size and life tenacity of the animal, but will be somewhat inversely proportional to the striking energy and momentum of the bullet provided that expansion and penetration are uniformly balanced.
The high striking velocities of today, contribute considerably to the rapid effects of the shot. These effects are many. The higher rotational speed of the missile increases the severity of the wound, because more tissue in its path is destroyed and it leaves a wider wound channel than the bullet can mechanically achieve. If small game is hit by a high velocity bullet, it may immediately be paralyzed by the impact, fall down and be unable to get up. A large game animal will not always react in the same way, even if hit by an extremely fast-moving bullet, but it is indisputable that velocity will to a large extent contribute to the effect of the shot.
The vital heart-lung area
Most shots at big-game animals are aimed behind the shoulder. A hit in the lung area with a modern soft-point hunting bullet will effect a quick kill even if the calibre used is not the heaviest of big-game cartridges. The lung function ceases immediately, no further oxygen enters the blood, the brain suffers from lack of oxygen and the animal expires mostly within 20-30 seconds. Since this can be achieved with a cartridge of moderate power, why are high energy cartridges recommended for big game hunting? A logical explanation may be:
If the bullet reaches and destroys central parts of the lungs, its power at that point is quite sufficient even if the cartridge used is relatively mild. The purpose is achieved just as well using say a .257 Roberts, as with a .30 Magnum. Even if you use the most powerful calibre available, but place the shot badly, the result on big game is more likely an extended and difficult tracking job and prolonged suffering for the animal, just as if you had hit it equally badly with a less powerful calibre. Thus, it is immaterial which calibre you have used, the purpose is not achieved in either case.
There is an advantage to using a heavier calibre since it provides an inbuilt safety margin. Where a smaller calibre of low energy and minimal shock effect would have resulted in a long often fruitless search, a calibre with energy to spare and higher striking velocities may mean that the animal will not run very far and can be quickly found and despatched.
Expansion and penetration
The essence of hunting is that game should be killed without unnecessary suffering. Vital, life sustaining organs should be destroyed as quickly and effectively as possible. In almost all big game hunting controlled-expansion bullets have proved superior. This type of bullet has a high residual weight which is a necessary aid for penetration. The better long range big-game loads utilize medium weight bullets driven at high velocity. Without producing excessive recoil, rifles chambering such loads are capable of sure-killing hits between 350 and 400 yards – much farther than the average hunter can reliably effect a hit with any rifle.
“Super magnums” that shoot heavy bullets at high velocity are deadly medicine. In the hands of a few seasoned marksmen such loads combined with precision rifles are the most effective long- range heavy-game propositions in existence; but not one shooter out of a thousand is able to make profitable use of them.
The efficient killing of deer-size game, taken-as-they-come, is supposed to be dependent on a striking energy of at least 1000 ft/lbs, with wapiti requiring at least 1500 ft/lbs. Whether or not you agree with these minimum energy figures, energy is only half the story. It has been established that reliable penetration of deer-size animals requires that bullets strike with a momentum figure which is equivalent to 240,000 arbitrary units. Momentum figures are calculated by multiplying the bullet’s weight in grains by the striking velocity in feet-per-second. Larger game, such as wapiti, sambar and moose require at least 360,000 relative momentum units. Momentum remains the same before and after impact.
The most reliable observers of killing power have concluded that kinetic energy is what determines a bullet’s total destructive ability – in volume of tissue destroyed – while momentum (aided by the bullet’s weight and construction), are the chief determinants of penetration. Therefore the bullet’s momentum and construction are what determines the depth of the wound, while its kinetic energy determines the extent (or volume) of the wound channel.
A bullet lacking only in energy may drill right through the animal with little tissue destruction, and may thus allow the wounded animal to run a long way before falling, often to survive and escape. The high-energy, low-momentum bullet, on the other hand, will destroy a lot of tissue but only to a comparatively shallow depth. Such a bullet usually kills spectacularly when placed squarely in the lungs, for instance, but often fails miserably when heavy bones or thick shoulder, neck or rump muscles are encountered on the way in.
Production of an adequate blood trail is one of a bullet’s most important functions, although this fact is seldom brought forcefully to the Ausie hunter’s attention. In open country a well-hit animal can usually be kept in sight until it falls, but if it manages to get into brush a copious blood trail is often needed to find it.
The average high-velocity addict seems to be totally unaware that momentum is necessary to penetration and that penetration is essential to reliable big-game shooting. Forget all that stuff you may have read on the internet about “shock waves” and “nerve paralysis”; the physical destruction which a bullet is capable of is purely a function of energy over a period of time. Velocity is part of the equation since it flattens trajectory and makes a contribution to energy. There may be certain nerve centres in vertebrate animals which react violently to velocity alone, but if they do exist they are so few in number that I’d not recommend the practical hunter take a chance on hitting one.