Columnist Col (Retd) EAS BOKHARI goes over the BALLISTICS thatdefines the penetration in muscle and bone of human beings, bullet wound statistics, and dispels some misunderstandings
|Ballistics is an arcane discipline - but somehow it has a very
considerable attraction for the gunners - and once you have been smitten by this
discipline - the wound remains with you for ever.
As a discipline ballistics is generally thought to be a discipline which deals with projectile flight - and other parameters such as air resistance - air density, gravitational pull et all - and a host of others which unfortunately have a bearing on the projectile flight and retard it from its ideal ie motion in 'vaccuo'.
But then there are such facets of ballistics like the ballistics of the meteorites, meteors - and other celestial breakaways - This celestial ballistics is very difficult as the parameters therein are not fed by man (but perhaps by providence). As basic ballistics may have internal, flight and terminal portions - the most important from the war fighting point of view being the terminal ballistics.
Unfortunately there has been a considerable debate and difference of opinion about the terminal ballistics of an ordinary bullet - which is the subject of this short presentation. The surgeon, the ballistician and the manufacturer have haggled about this effect (ie the terminal effect) which has been erroneously thought to be a function of the muzzle velocity. This unfortunately is not quite true. This short piece should provide a profitable ground for the surgeon - the ballistician and the manufacturer to understand each other on the issue of bullet ballistician.
Among the deadly weapons like missiles and rockets that saturate the modern battlefield, one tends to under-rate the bullet and the bayonet. The ballistics of bullet, however, makes a very interesting study although there is considerable disagreement among surgeons, ballistic experts and the manufacturers of bullets on the finer points, particularly on the nature of the bullet wound and how best it should be treated. Wound ballistic, therefore, is as important today as it was in the last century. This short presentation is devoted to wound ballistics and has been gleaned from an International Defence Review (IDR) forum held in Geneva.
Wound ballistics is an old discipline yet more than 80 percent of what was written about wound ballistics whether or not by experts was false; many misconceptions arose from the tunnel vision of ammunition designers and surgeons who had only a partial understanding of each other's disciplines. When the subject was reported on by journalists with no understanding of either field, the problems were compounded. It is intended to bring out some of the fallacies which had been taken as a gospel without checking these empirically or scientifically. Some of the points that came out of the Geneva Forum, which was dominated by Col. Fackler, are summarised below:
According to Col. Fackler wound ballistics is the science which deals with the interaction of penetrating projectiles and living tissue so when the ammunition designer does his best to design projectiles to disrupt tissues, the surgeon does his own best to repair those. First a few simple clarifications. The main aim of a bullet is to crush, i.e., destroy the tissue actually hit by the bullet, and stretch which is the transient/radial displacement of adjacent tissues in the wake of the projectile. The wound path of the projectile is known as permanent cavity and the stretching is known as temporary cavity. (See diagram).
According to Col. Fackler it is the permanent cavity which represents the wound mechanism, and the wounding effects of the temporary cavity are generally exaggerated. For example, some of the human parts like lungs, blood vessels bowel walls, etc., are elastic enough and tolerate stretching. Of course, solid tissue such as liver may not be so resilient.
There is a general impression that sonic waves set up by relatively high speed bullets could kill by damaging a large number of nerves through shock. This was refuted by Col. Fackler who opined that there was no solid evidence for this conclusion as the pressure peak of about 100 atmospheres had a duration of only two microseconds. It, therefore, did not move or harm the tissues.
There are two very common misconceptions about the temporary cavity. The first one being that the tissue adjacent to the projectile path was forced aside at a speed equivalent to that of the bullet or even greater. By measuring the distance travelled by the projectile and comparing it to that travelled by the walls of temporary cavity, it is found that the tissue is displaced at a speed less than one-tenth of the projectile. The second misconception is that high velocity bullets cause temporary cavities 30 times the diameter of a bullet. As a result of Swedish studies it has come out that at a velocity of I Km/second, a temporary cavity of II diameters is possible and not more. For a 30 times bigger cavity than the projectile a speed of 2 Km/second is needed which is not encountered in actual battlefield. It was also brought out that the best test media should be large animals, i.e., those with comparable weight with human beings and not 'mini pigs' which are often used, and which provide erroneous results.
There is considerable vagueness about the classification of bullets into low and high velocity. For one European high velocity indicated the 5.56 mm rifles of the last 20 years with a muzzle velocity of around 900 m/s. In America, it is thought that the term denoted a muzzle velocity of 700-800 m/s. Yet there were people who defined it as 900 m/s while others bestowed the term on any projectile with a speed of more than 300 m/s - so all this is not very precise.
The real fact is that the wound size may be independent of the muzzle velocity. For example, the bullet of mid to late 19th century had the velocity of around 400 m/s (which is low by present standards), but it produced large permanent and temporary cavities as the bullet was made of lead which deformed on striking the target, thus increasing its area and capacity for tissue disruption while the high mass ensured that it retained its capacity to penetrate.
It is noticed that a generation of rifles which were 50 per cent higher in muzzle velocity in fact produced a lower wounding capacity as these used jacketed bullets which did not deform on compact. The fact is that the real parameters which one should look for in a rifle are both the mass and the velocity of the bullet -and not velocity alone at the point of impact. To quote Col Fackler, The potential for tissue disruption depends on mass and velocity realisation depends on bullet construction, shape and interaction with target tissue, the type of tissue it hits. You can't say that a certain velocity in every case will give an X amount of damage. The high velocity shibboleth in fact have given the surgeons a wrong attitude to bullet wounds while de-bridging those which are sometimes excised rather than cured - which in fact does more harm than good. Surgeons should not fix what ain't broke but instead treat the wound, not the weapon.
It also came out very clearly in the discussion that the kinetic energy transfer was not a mechanism of injury as were the crushing and stretching of tissues, and the amount of kinetic energy deposited or the bullet's striking velocity were not reliable indicators of the wound severity.
The discussion later dwelt on the current crop of the Assault rifles, i.e., the Soviet AK-74 and the US M-16. In sum, the Soviet bullet is highly effective though it also does not deform on impact. What in fact happens in the Soviet bullet is that on impact the lead flowed forward into the air gaps to produce a bullet whose mass was distributed asymmetrically. This combined with the fact that the air gap placed the bullet's centre of gravity well back was the reason for its early yaw in tissue producing a large permanent cavity even in extremity shots. (See diagram).
The American bullet did not do so well, and the M-193 bullet fired by the M-16. AI rifle travelled point first through tissue from some 12 cm before yawing. This could result in relatively little damage in shots through limbs where the wound track is short. The M-16, however, did fragment in some way which perforated wounds away from the main cavity.
Finally, the ballistics of wounds is not really well understood even now and the surgeon and ballistic expert have their own concepts, and only an extensive data base can provide accurate answers to bullet design and wound treatment.