Terminal Ballistics - Getting Past the BS
By Adam Gubar
Any discussion of terminal ballistics is a world unto itself, part science, part art, part intuition, part myth and voodoo. Perhaps no other topic in shooting and firearms elicits stronger emotion than the question of which bullet is better for a given task. Wading through these murky waters is tenuous at best. While the possible combinations of bullet caliber, weight, form, construction and speed can seem daunting, it is possible to boil it all down to a few basic principles.
The first thing to understand is that there are basically two broad schools of thought with regards to terminal ballistics, or the performance of the bullet inside an animal, that tend to dominate popular thought. We can lovingly refer to these two groups as the Speed Freaks and the Size Kings. The first believes the velocity of the projectile is the most important factor in killing power, often to the exclusion of many other variables. This camp also includes those who extol the virtues of energy delivered on target. The other faction places size pre-eminently in their estimation, also to the common exclusion of many other factors. Size is normally a reference to bullet diameter (caliber), bullet weight (in grains), or both.
This includes those who are constantly seeking the ultimate magnum. They will often throw around terms like "temporary wound cavity," "energy dump" and "hydrostatic shock." Following is the basic steroidal velocity argument, as I understand it:
∑ Fast bullets penetrate deeper.
The problem is that most hunters (unless hunting very large, thick-skinned animals like elephant, rhino or Cape buffalo) use some form of expanding bullet. The faster a bullet is moving, the faster it expands. The faster the bullet expands, the more frontal area, and hence resistance it encounters moving through a target. The more resistance, the more speed is bled off and the less penetration the bullet achieves. Ergo, fast expanding bullets penetrate less than fast solid bullets.
∑ Fast bullets create a larger temporary wound cavity
Temporary wound cavity, which can be clearly visualized in ballistic gelatin viewed through slow-motion or stop-motion photography, is like the air turbulence around a plane. Once the plane moves on, the displaced air settles back into where it was. Flesh does much the same thing as a bullet passes through it. Flesh is roughly 75% water (most organs included) and will stretch and/or compress up to 12 inches on average before it tears. As flesh is violently displaced around the path of a bullet, it stretches and compresses the area around it, then snaps back just as violently.
∑ Fast bullets have a greater chance of producing "hydrostatic shock"
The myth of hydrostatic shock is that, as a bullet passes through flesh, it creates a pressure wave which can rupture organs, disrupt blood flow and short out synaptic function in the brain and central nervous system. For the same reasons that temporary wound cavity can not, generally speaking, cause death, so too does hydroshock fall short. Yet despite this, proponents will trot out legendary cases of a gut shot 300 pound caribou that took two steps and fell over dead. Unfortunately, many of these incidents cannot be confirmed and after myriad attempts, the effect cannot be reliably reproduced in test animals. The closest scientific evidence of distant damage from peripheral wounding comes from the shrapnel of fragmented projectiles and bone which travel through the body and damage vital organs. The physics are such that an energy wave capable of actually turning a target off like a switch would require a large pressure wave similar to that produced by a high explosive force.
∑ Fast bullets deliver more kinetic energy on target
Some Speed Freaks will eschew through-and-through penetration in lieu of something called "energy dump." The idea is that the most efficient bullet is one that stops just inside the hide on the far side of the animal, so that all of its kinetic energy has been expended in the animal. Here's the long and short of it. A standard NATO 5.56 round with a mass of between 50 and 60 grains has approximately the same kinetic energy as a 75mph fast ball, or a copy of War and Peace falling off a table. There is not enough kinetic energy alone in a bullet to kill. (Energy powers both bullet expansion and penetration, though, which means it powers the mechanisms that do kill. - Editor.)
These guys generally believe that a clean kill is dependent on having larger, heavier bullets. They will talk about things like frontal area, meplat and momentum. The bullet obesity idolaters sound something like this:
∑ The larger the bullet, the larger the hole and more blood loss.
This is actually not an incorrect statement, if you are dealing with non-expanding (solid) bullets. Unfortunately, some of those espousing it are often using it to justify poor shot placement. They will claim that if the shot misses the engine works of lungs and heart, the larger wound cavity means the animal will bleed out faster and die sooner. Thatís lovely, but it is not good, per se. It suggests that close is good enough, if you have a large enough projectile. This may apply to artillery fire, but not humane hunting. (In the real world, a gut shot elk or a deer with a broken leg will eventually die, but is unlikely to be recovered by the hunter, whether it was wounded with a .243 or a .458. -Editor.)
∑ More mass means better penetration
This fails to recognize that, even with non-expanding bullets, it is sectional density that actually determines penetration (assuming all other factors are equal). The big bullet true believers also tend to ignore bullet construction. The vast majority of hunting bullets are expanding, which militates against penetration. As well, without sufficient impact velocity and energy, mass is moot as regards penetration. This goes back to the basic energy example given previously. A 75 mph fast ball or a book falling 3-4 feet will not penetrate the side of an animal, even though the baseball would weigh about 3,200 grains and a hardbound War and Peace would tip the scales at about 35,000 grains.
∑ Lower velocity actually produces more penetration
This has been going around for years now, where size kings will reference tests done in different types of media where the same bullet (typically a hard cast lead alloy or steel jacketed solid) fired from a .45-70 at 1500 fps had nearly twice the penetration of a .458 Win. Mag. moving at 2300 fps, which in turn penetrates 20% deeper than a .458 Lott moving at 2500 fps. These ďtestsĒ all have the same basic flaws. First, the media used is typically either wet newspaper that has almost none of the fluid dynamics of flesh, or water jugs that have one tenth the density, surface tension and resistance of flesh. Neither can approximate real world effects. The problem with wet newspaper is that the faster bullets will flatten out and/or deform very rapidly, which makes them react like an expanding bullet. The problem with the water lies in the fact that the faster bullets are almost always accompanied by faster twist rates. This means that the bullet is turning faster. In air, the bulletís spin causes a slight lift and turn in the direction of spin over great distances. This is called gyroscopic drift, something long range shooters and snipers must take into account. In water, because of the nature of the media, destabilizing factors on the yaw of the projectile called Magnus Effect and Poisson Effect actually pull the bullet off axis faster as the bullet noses into the spin. This means that while the bullet will seem to penetrate less deeply, it actually has traveled further, taking a squiggling, corkscrew route.
∑ The larger the meplat, the more tissue damage
The meplat is the flat face of a flat-nose, truncated, or semi-wadcutter style bullet. This statement, like a couple before it, may have some validity if applied only to non-expanding bullets. However, it is another example of math in a vacuum. First, meplats are only present in a few bullets, usually solid or cast lead types. (A .30-30 jacketed flat point bullet would be the most common exception.) Typical expanding hunting bullets have round, pointed or hollow pointed shapes and so do not have meplats. Also, as is the problem with expansion, a larger meplat creates more resistance as it moves through the target, which decreases speed more rapidly, thereby reducing penetration and resulting in a shorter permanent crush cavity.
∑ The greater the cross-sectional area, the more tissue damage
This is the same as the previous, but is argued by those who are speaking about expanding projectiles. However, when referring to expanding bullets, the slower speed of a larger, heavier projectile can mean that the bullet does not expand properly and certainly less than an equivalent bullet at higher velocity. This lack of expansion would increase penetration, but would do nothing for the size of the wound channel, which is the basis of the cannonball worshipperís argument.
While this civil war continues to rage in the gun press, certain African countries, dependent on tourism revenue, have gotten on board with one theory or another. In an attempt to create certain safety standards and reduce liability claims against guides and outfitters, these nations have established minimums for hunting large and dangerous animals. In some African nations, this has been set forth as a minimum caliber of .375 inch or 9.3mm. In others, it has been stated as a projectile with a minimum of 4000 foot-pounds of kinetic energy at the muzzle.
To be sure, there are a plethora of methods, both pseudo-scientific and otherwise, of ďprovingĒ each of these beliefs. Calculations such as Optimum Game Weight, Taylor Knockout Power, Thornily Relative Stopping Power and a dozen more all claim to offer a relative comparison of the effectiveness of different calibers and loads. Each will overweight in some way the factor the originator believes to be of paramount importance, be it speed, size or mass. Each fits neatly into a chart to show that a .505 Gibbs is a more powerful cartridge than a .30-30.
The truth is that the single most important factor in the lethality of any bullet is shot placement. This is determined primarily by trigger control, breath control, a steady shooting position, a calm mind, rifle recoil that is well within the shooter's tolerance, a clear and visible target at a range within the shooter's ability that is free of obstacles that might deflect the bullet and negligible wind. Plus, of course, practice; lots and lots of practice.
There are certain factors that can help a shooter determine the efficiency of different calibers or classes of calibers versus different types of game. For this, we must start by breaking down the different types of game and ranges. An excellent starting point for this can be found right here on Guns and Shooting Online, such as "CXP Rating System for Hunting Cartridges" by Chuck Hawks. Similar information is also included in many ammo catalogs (Winchester, Federal, Hornady and Weatherby, for instance).
Next, it is necessary to consider what factors affect terminal ballistics beyond shot placement, such as penetration, deflection, bullet construction and permanent wound channel.
Penetration is compared by the bulletís sectional density, or ratio of mass to frontal area. The higher the sectional density, the deeper the penetration, given a non-expanding bullet. Two excellent articles for determining appropriate SD are "Sectional Density for Beginners" by Bob Beers and "The Sectional Density of Rifle Bullets" by Chuck Hawks.
Deflection is compared by the bulletís momentum, which is determined by mass and velocity. Higher momentum implies less deflection when a bulletís path takes it in contact with bone, cartilage or tendons. Higher momentum indicates a likelihood a projectile will shatter heavy bone and pass through, rather than vise versa.
Permanent wound channel is the crush cavity, the path of destruction left after a bulletís passing. The larger the permanent wound channel, the more damage is done to incapacitate vital organs. Even with non-expanding bullets, the permanent wound channel will typically be larger than the diameter of the projectile. This is due to many factors, but primarily twist, yaw and tumble, spall, pressure and the effect of the temporary wound cavity. As a bullet passes through flesh, its spin will twist the flesh, causing tears. Likewise, yaw--the off-axis movement of the nose of the projectile--and tumble cause damage in a wider path. Spall is the fragmenting that occurs as the bullet loses mass to the surrounding tissue. Finally, the pressure built up in front of the bullet can effectively cause the skin or hide on the far side to violently rupture, leaving a much larger exit wound than entrance wound.
Bullet construction includes expanding, controlled expanding and non-expanding bullets. The faster a bullet expands the less penetration it will achieve, but the diameter of the permanent crush cavity is increased. Similarly, larger meplats of solid and cast bullets create a larger permanent wound channel than spitzer, or pointed, bullets, but at the cost of some small measure of penetration. However, the less pointed a bulletís nose profile, the less deflection it is susceptible to in its course. Non-expanding spitzer bullets and some controlled expansion bullets reaching a target at too slow a speed to reliably open are often the most susceptible to tumbling in an animal. Rapidly expanding bullets with a soft core at high impact velocity will tend to fragment or shatter readily. This is why they are preferred by varmint shooters.
Stronger bullet construction, using tapered jackets, thicker jackets, harder lead cores, partitions, bonding and the like, reduces expansion and prevents most fragmentation, but such bullets do not expand as rapidly, particularly in light framed animals like deer, as simple soft point bullets with thin jackets. Some manufacturers compensate for this slower expansion with plastic inserts (Balllistic Tip) in the bullet's nose to initiate expansion. This is similar in function to a hollow point. Others add stress points or relief cuts in the front of the bullet jacket to aid expansion (Power Point). Regardless, the slower expansion is of particular value at high impact velocity, where controlled expansion bullets usually open reliably and provide adequate penetration.
Solid bullets, those with relatively hard cores and thick jacketing that covers at least the entire nose and sides of the bullet, are not entirely immune from distortion. These bullets have been known to tumble, flatten, bend, rivet, spew their cores or otherwise deform. This affects not only penetration, but also bullet path. However, these problems are less common with modern homogeneous or very heavily jacketed, bonded core solids. (Solid, FMJ and similar non-expanding bullets may be suitable for use on African or Asian CXP4 game, but are illegal for hunting in most North American jurisdictions. This is because they have proven to be great wounders and poor killers of animals like deer, black bear and elk. - Editor.)
Generally speaking, the factors that are desirable in external ballistics, the flight of the bullet to the target, are the opposite of what is desirable in terminal ballistics. A highly aerodynamic, weight rearward projectile will reach the target quickly and accurately. However, a blunted or mushroomed, weight forward projectile will do more immediate damage once it impacts the animal.
PUTTING IT ALL TOGETHER
So, what is the best bullet in the best caliber in the best rifle for taking down any animal? Itís the one the shooter can consistently put on target. Everything else is gravy. That said, hereís a summary.
There is no magic formula for the perfect kill, despite what many gun writers would suggest. Much of what is written is done to sell advertising and promote products. When the fascination with speed and size are removed from the decision making process, what remains is a moderated discussion about what is most appropriate for the type of game and the individual shooter's needs. In the end, that is the conversation worth having.
Copyright 2012 by Adam Gubar and/or chuckhawks.com. All rights reserved.