Introduction
Whether we like to admit it or not, the primary purpose of
military rifle bullets is to disrupt human tissue. Yet the effects of bullets on bodies --
the characteristic tissue disruption patterns produced by various bullets -- remains
unclear even to many of those who design and produce bullets. Surgeons who are called upon
to treat the damage bullets cause, with few exceptions, lack practical knowledge of bullet
effects. Attempts to fill this information void with formulae, graphs, flawed experiments,
invalid assumptions, and theories based on half-truth (or no truth at all) have only
increased confusion.
The obvious -- simply measuring, recording and describing the
disruption produced by various calibres and bullet types -- has largely been ignored in
favour of more dramatic and complex methodology. To illustrate the problem: if a neighbour
told you that a meteorite had fallen into his back yard, wouldn't you ask him how deep and
how large a hole it had made? If he replied that he had, on good authority, an estimation
of the meteor's striking velocity and the amount of kinetic energy it had
"deposited" and gave you both these figures, you might be impressed by the
sophistication of this information, but you still wouldn't know how big a hole he had in
his yard.
Roger Frost, in his cogent editorial "Bullet holes in
theories" (IDR 8/1988 p.875) suggested that the various groups interested in gunshot
wounds need to "start talking to one another". Let's add that the talk needs to
be in terms that can be understood by all -- to inform rather than to impress.
In order to illustrate the penetrating projectile-body
tissue interaction, the "wound profile" method was developed. It is an attempt
to present a useful approximation of the pertinent, useful, factual data to clarify bullet
effects in a form that can be readily understood. The profiles depict the maximum
disruption that a given bullet can be expected to produce in the elastic soft tissue of
the living animal. The "permanent cavity" indicated on the wound profiles is the
"bullethole" produced by the projectile crushing the tissue it strikes. The
"temporary cavity" shows the approximate extent to which the walls of this hole
were stretched a few milliseconds after bullet passage (entirely analogous to a splash in
water).
Anyone who has ever seen a bullet hole recognises that in
many cases it is, in fact, more what might be called a potential hole; it need not be
gaping open. One can, however, easily pass a probe through it, as is commonly done by
forensic pathologists to establish the direction or angle of the shot. How deeply the
bullet penetrated and its attitude (yawed or straight) and form (deformed or fragmented)
as it penetrated, along with the approximate distance the walls of the hole were stretched
after the bullet passed (temporary cavity) -- this is the crucial information needed to
understand the wounding mechanisms.
To describe wounding patterns of the common military rifle
bullets in use today, wound profiles will be used along with a description of the two
characteristic wounds for each bullet. A simple abdominal wound, and an uncomplicated
(didn't hit bone or large vessels) human thigh wound caused by each bullet will be
described to demonstrate how the material presented as wound profiles can be put to
practical use. This should give the combat surgeon some idea of what to expect. His
descriptions of the wounds he actually treats, if they differ significantly from the
expected pattern, might be the first indication of a change in enemy weapon or bullet
type. Patterns of bullet fragmentation as seen on x-ray, or even the tissue disruption
pattern as observed in the body, can be compared with the series of wound profiles to
estimate the bullet type when the bullet has passed entirely through.
Soviet 7.62x39mm -- The Soviet AK-47 Kalashnikov fires a
full-metal-jacketed, boat-tail bullet that has a copper-plated steel jacket, a large steel
core, and some lead between the two. In tissue, this bullet typically travels for about
26cm point-forward before beginning significant yaw. This author observed, on many
occasions, the damage pattern shown in Fig. 2 while treating battle casualties in Da Nang,
Vietnam (1968). The typical path through the abdomen caused minimal disruption; holes in
organs were similar to those caused by a non-hollow-point handgun bullet. The average
uncomplicated thigh wound was about what one would expect from a low-powered handgun: a
small, punctate entrance and exit wound with minimal intervening muscle disruption.
Yugoslav 7.62x39mm -- The Yugoslav copper-jacketed,
lead-core, flat-base bullet, even when fired from the same Kalashnikov assault rifle, acts
very differently in tissue. It typically travels point-forward for only about 9cm before
yawing. Due to the lead core, this bullet flattens somewhat as it yaws, squeezing a few
small lead fragments out at its open base, but this does not add significantly to its
wounding potential. Referring to the wound profile of the Soviet AK-47 bullet (Fig. 2) and
blotting out the first 17cm of the projectile path will leave a good approximation of what
one might expect from this bullet.
Since this bullet would be travelling sideways through most
of its path in an abdominal wound, it would be expected to cut a swath over three times
the dimension made by the bullet travelling point forward. In addition to the larger hole
in organs from the sideways-travelling bullet, the tissue surrounding the bullet path will
be stretched considerably from temporary cavitation. Actual damage from the stretch of
cavitation can vary from an almost explosive effect, widely splitting a solid organ such
as the liver, or a hollow one such as the bladder if it is full at the time it is hit, to
almost no observable effect if the hollow organs (such as intestines) when hit contain
little liquid and/or air. The exit wound may be punctate or oblong, depending on the
bullet's orientation as it struck the abdominal wall at the exit point. The exit wound
could be stellate if sufficient wounding potential remains at this point on the bullet
path. The thigh entrance wound will be small and punctate but the exit wound will probably
be stellate, measuring up to 11 cm from the tips of opposing splits. The stellate exit
wound results from the temporary cavity simply stretching the skin beyond its breaking
point. These stellate wounds generally bleed very little. Small-to medium-sized vessels
are certainly cut or torn, but the temporary cavity tearing action generally stimulates
the tiny muscles in the vessel walls to constrict and clots will form in their open ends,
limiting blood loss. Being wide open, these wounds tend to drain and heal amazingly well
even in situations of limited surgical resources. This increased tissue disruption of the
leg will, of course, temporarily limit the mobility of the person hit to a greater extent
than wounds causing less tissue disruption.
Soviet 5.45x39mm -- This is fired from the AK-74, which is
the Soviet contribution to the new generation of smaller-calibre assault rifles and which
produces the wound profile seen in Fig. 3. The full metal-jacketed bullet designed for
this weapon has a copper-plated steel jacket and a largely steel core, as does the bullet
of its predecessor, the AK-47. A unique design feature of the AK-74, however, is an
air-space (about 5mm long) inside the jacket at the bullet's tip (Fig 1). The speculation
that this air-space would cause bullet deformation and fragmentation on impact proved to
be unfounded, but the air-space does serve to shift the builet's centre of mass toward the
rear, possibly contributing to its very early yaw. In addition, on bullet impact with
tissue, the lead just behind the air-space shifts forward into this space. This shift of
lead occurs asymmetrically and may be one reason for the peculiar curvature of this
bullet's path in the last half of its path through tissue (Fig 3). Only in a shot with a
long tissue path, like an oblique shot through the torso, would this curved path be
evident; it doesn't really add anything to wounding capacity, but might cause an
occasional confusing path through tissue. This bullet yaws after only about 7cm of tissue
penetration, assuring an increased temporary cavity stretch disruption in a higher
percentage of extremity hits; other bullets need more tissue depth to yaw and in many
cases cause only minimal disruption on extremity hits.
The abdomen and thigh wounds expected from this bullet would
be essentially the same as those described above for the Yugoslav variation of the AK-47
bullet.
All pointed bullets that do not deform end their tissue path
travelling base first, since this puts their centre of mass forward; this is their stable
attitude. The rotation imparted to the bullet by the rifled gun barrel is sufficient to
force the bullet to travel point-forward in air (in properly designed weapons), but not in
tissue where such factors as bullet shape and the location of centre of mass far outweigh
rotation effects. The bi-lobed yaw patterns shown in the profiles of the AK-47 and the
AK-74 represent what is seen in most shots. Sometimes the bullet yaws to 180°, or the
base-forward position, in one cycle. These variations, along with the curvature in bullet
path at or near the end of tissue path, are of far less importance than the distance the
bullet travels point-forward before significant yaw begins.
USA M193 5.56x45mm NATO -- This bullet is fired from the US armed
forces' first-generation smaller-calibre rifle, the M16A1. The large permanent cavity it
produces, shown in the wound profile (Fig. 4), was observed by surgeons who served in
Vietnam, but the tissue disruption mechanism responsible was not clear until the
importance of bullet fragmentation as a cause of tissue disruption was worked out and
described. As shown on the wound profile, this full-metal-jacketed bullet travels
point-forward in tissue for about 12cm after which it yaws to 90°, flattens, and breaks
at the cannelure (groove around bullet midsection into which the cartridge neck is
crimped). The bullet point flattens but remains in one piece, retaining about 60 per cent
of the original bullet weight. The rear portion breaks into many fragments that penetrate
up to 7cm radially from the bullet path. The temporary cavity stretch, its effect
increased by perforation and weakening of the tissue by fragments, then causes a much
enlarged permanent cavity by detaching tissue pieces. The degree of bullet fragmentation
decreases with increased shooting distance (as striking velocity decreases), as shown in
Fig. 5. At a shooting distance over about 100m the bullet breaks at the cannelure, forming
two large fragments and, at over 200m, it no longer breaks, although it continues to
flatten somewhat, until 400m. This consistent change in deformation/fragmentation pattern
has an important forensic application. It can be used to estimate shooting distance if the
bullet is recovered in the body and has penetrated only soft tissue.
The effects of this bullet in the abdomen shot will show the
temporary cavity effects as described for the Yugoslav AK-47 and, in addition, there will
be an increased tissue disruption from the synergistic effect of temporary cavitation
acting on tissue that has been weakened by bullet fragmentation. Instead of finding a hole
consistent with the size of the bullet in hollow organs such as the intestine, we
typically find a hole left by missing tissue of up to 7cm in diameter (see permanent
cavity in Fig. 4). The thigh entrance wound will be small and punctate. The first part of
the tissue path will show minimal disruption. The exit will vary from the small punctate
hole described for the Soviet AK-47 to the stellate exit described for the Yugoslav AK-47,
depending on how thick the thigh is where the bullet perforates it. In a sufficiently
thick thigh, the M193 bullet fragmentation is also likely to cause a significant loss of
tissue and possibly one or more small exit wounds near the large stellate one.
M855/SS109 5.56x45mm NATO -- The slightly heavier and longer
American M855 bullet shot from the M16A2 assault rifle is replacing the M193 bullet shot
from the M16A1 as the standard bullet of the US armed forces. FN Herstal originally
developed this bullet type (which has a steel "penetrator" as the forward part
of its core -- Fig. 1) designating its bullet the SS109. The wound profile (Fig. 6) is very
similar to that produced by the M193 bullet. Although the SS109 and the M855 are not the
same bullet, their differences are small and one almost needs a magnifying glass and a
side-by-side comparison to differentiate the two. There is little difference in their
performance in tissue.
The abdominal and the thigh wound produced by the M855 or
the SS109 bullets would be essentially the same as those described above for the M16A1
M193 bullet.
The longer 5.56mm bullets (M855, SS109) need a higher
rotational velocity to maintain stabilisation in air. FN claimed that this faster rotation
also causes the SS109 to have a significantly longer path in tissue before marked yaw
occurs, thus producing wounds of less severity. This is simply untrue (compare Fig. 6 with
Fig. 4). Additional rotation beyond that needed to keep the bullet straight in air appears
to have little or no effect on the projectile's behaviour in tissue. However, there is a
situation concerning rotation rates whereby these longer 5.56mm bullets can cause
increased wound severity. Shooting the SS109 or M855 bullet in the older M16A1 rifle
barrel (they are not intended for use in this 7-in-72-inch twist barrel, but in the newer M16A2
1-in-7-inch twist) produces a bullet spin rate insufficient to stabilise the longer
bullets. Such a bullet will yaw up to 70° in its path through air. Striking at this high
yaw angle (essentially travelling sideways), these bullets break on contact and the marked
fragmentation, acting in synergy with the temporary cavity stretch, causes a large (over
15cm) stellate wound with the loss of considerable tissue (Fackler, M.L., unpublished
data, 1988).
M80 7.62x51mm NATO (US version) -- The wound profile of this
full-metal-jacketed military bullet (Fig. 7) shows the characteristic behaviour in tissue
observed in all non-deforming pointed bullets. It yaws first through 90° and then, after
reaching the base-forward position continues the rest of its path with little or no yaw.
The uncomplicated thigh wound might show very minimal tissue
disruption since the streamlined bullet tends to travel point forward during the first
16cm of its tissue path. The abdominal wound, with a sufficiently long path so that the
bullet will yaw, causing the large temporary cavity that is seen at depths of 20 to 35cm,
would be expected to be very disruptive. If the bullet path is such that this temporary
cavity occurs in the liver, this amount of tissue disruption is likely to make survival
improbable.
7.62x51mm NATO (West German version) -- The design standards
for ammunition that can be called "NATO" ammunition do not specify bullet jacket
material or jacket thickness. The construction of the West German 7.62 NATO bullet differs
from the US 7.62 NATO round in that the jacket material is copper plated steel, whereas
the US version is copper (or the so called gilding metal alloy, which is predominantly
copper). The West German steel jacket is about 0.020in (0.6mm) thick near the cannelure
and the US copper jacket is about 0.032in (0.8mm) thick at the same point. This design
difference is responsible for a vast difference in performance in tissue. The German
bullet, after travelling point-forward for only about 8cm, yaws and breaks at the
cannelure. The flattened point section retains only about 66 percent of the bullet's
weight, the remaining 45 per cent becomes fragments (Fig. 8). The wound profile can be
described as an enlarged M16 profile (Fig. 3), with dimensions of the tissue disruption
increased by 60 per cent (temporary cavity about 22cm diameter; permanent cavity about 11
cm diameter, penetration depth of the bullet point about 58cm).
The uncomplicated thigh wound from this bullet is likely to
have a large exit with the loss of substantial tissue near the exit; still, this might not
be a very serious wound since the bullet fragmentation does not occur until beyond 10cm of
penetration depth and, in most shots, the bullet will have passed well beyond the major
vessels before this occurs. The abdomen shot, however, because of the much enlarged
permanent cavity from bullet fragmentation, is likely to prove fatal in a majority of
cases.
Overview
In addition to the full-metal-jacketed construction which
makes them "military" bullets, the pointed ogival "spitzer" tip shape
is shared by all modern military bullets. The obvious advantage of this streamlined shape
is decreased air drag, allowing the bullet to retain velocity better for improved
long-range performance. A modern military 7.62mm bullet (with all-lead core) will lose
only about one-third of its muzzle velocity over 600 yards (467m); the same weight bullet
with a round-nose shape loses more than one-half of its velocity over the same distance.
More pertinent to the present discussion is this pointed
shape's effect on the bullet's yaw in tissue. The first full-metal-jacketed bullets
(1885-1910) were over four calibres long and round-nosed. Typical of this bullet type are
the 6.5mm Carcano and the 30-40 Krag bullets; they penetrate tissue simulant travelling
point-forward for 50cm or more before significant yaw begins (Fackler, M.L., unpublished
data, 1987). The very minimal wounding effect produced by these early round-nosed jacketed
bullets was remarked upon by surgeons of the time (Kocher, Markins, Brunner, Abbott,
LaGarde, etc.). Even those soldiers with through-and-through chest wounds in which the
bullet missed the large vessels (but passed through the lung) would be fit to rejoin their
units in a few weeks.
The distance that the military-type bullet travels
point-forward before yawing is critical to wounding effects. The distance shown on the
wound profiles is the average distance at which this occurs. However, it is important to
recognise how much shot-to-shot variation from this average distance can be expected.
Taking the M16 wound profile (Fig. 6) as an example, it shows significant yaw starting at
a 12cm penetration depth. Seven out of ten shots can be expected to begin yaw within 26
per cent of this distance (between nine and 16cm penetration depth). This plus or minus 25
per cent rule is a useful approximation that can be applied to the otherwound profiles.
Let us apply it to the 50cm distance-to- yaw for the older bullets; whether the bullet
begins to yaw between 37 or 63cm penetration distance does not effect most wounds of the
human body because, in the great majority of cases, the total tissue path will be less
than 37cm.
Conversely, inconsistent effects have been noted in wounds
caused by the M16 and other modern military bullets. Considering the variation in length
of the possible tissue path through the human body, this "inconsistency" of
effect is to be expected. Beware! This variation can be used to dupe the unsuspecting. A
series of shots through a 14 or 15cm block of tissue simulant or the leg of a 25kg animal
can give enough variation so that, by selective choice of exit wound photographs, one can
"prove" any point one wishes (such as one bullet being less "humane"
than another). The author hopes that understanding this will make the reader less likely
prey to this sort of deception.
Bullet mass and bullet striking velocity establish a
bullet's potential; they set the limit on the tissue disruption it can produce. Bullet
shape and construction determine how much of this potential is actually used to disrupt
tissue; they are the major determinants of bullet effect. Far and away the most disruptive
bullet of those described is the West German 7.62x51mm NATO round. Its fragmenting behavior
maximises utilisation of its much higher potential (bullet mass well over twice that of
any of the 5.56mm bullets and velocity only about ten percent less than theirs) for tissue
disruption.
This author has not tested other European 7.62 NATO rounds,
but the "NATO standards" apparently allow bullet designers great latitude in the
choice of bullet jacket material and thickness. In 1979 a published high-speed x-ray
photograph showed the Swedish 7.62 equivalent to the 7.62 NATO bullet breaking in a soap
block shot at a range of 100m. Although bullet fragments were not recovered and
photographed (the importance of bullet fragmentation in tissue disruption was not well
recognised at the time), one must suspect the same very disruptive behaviour from this
bullet as from the West German round. This is particularly ironic since the Swedish wound
ballistics program was using every means possible to discredit the M16 as
"inhumane" while, at the same time, Sweden was producing a 7.62mm military bullet
that caused far more extensive wounds than the M16.
Future Combat Rifle Considerations
Two concepts that are being considered deserve comment.
First, the flechette (a nail with fins) used as a single small-arm projectile: this
projectile has been used in artillery rounds to increase the radius of the injury zone. It
retains velocity well due to its aerodynamic shape and high length-to-diameter ratio. It
can cause wounds at a much greater distance from the detonation than blunt irregular
fragments or spheres that lose velocity rapidly. However, an overwhelming limitation of
the flechette is the very minimal wound it causes. Flechettes are stabilised in air by
fins rather than rotation. Fin stabilisation works just as well in tissue, keeping the
projectile point forward. Travelling in this attitude, it causes minimal tissue crush
disruption and almost no temporary cavity.
Military rifle bullets yaw in tissue because their rotation
is sufficient to maintain their point-forward travel in air, but insufficient to maintain
that position in tissue -- sooner or later they yaw to reach their stable
centre-of-mass-forward attitude. Flechettes have the drag of the fins permanently attached
on their tail to keep the point forward; this stabilises them in air and in tissue.
Considerable confusion exists concerning the effects of
flechettes. In a recent publication one finds the erroneous statement "...the
flechette can inflict severe wounds by virtue of its poor stabilisation and readiness to
tumble on impact...". Bellamy's "Little arrows", the classic paper on
flechettes, points out a reason for the misconceptions: Many flechettes launched from
artillery shells are bent by the force of the detonation. Persons close to the detonation
are penetrated by these bent flechettes. It has been assumed that the bending resulted
from the flechettes striking the body. Bellamy's report is in accord with this author's
personal experience treating flechette wounds on the battlefield -- flechettes, as used
thus far in warfare, travel straight in tissue and cause very minimal tissue disruption.
The second consideration is the use of the three-round burst
at a rate of fire of 2,000 rounds per minute in the Heckler & Koch G11 caseless ammunition rifle.
This burst fire and high cyclic rate are designed to increase hit probability. This may be
a significant factor in the weapon's effectiveness at ranges over 200m, where only one of
the three rounds is likely to hit. What, however, will be the wounding effect of this
three-round burst at ranges under 50m where most of the casualties have occurred in recent
conflicts? At this range the three rounds will hit the body within a few centimetres of
one another; each successive round will hit within 30 milliseconds of the previous one.
The first temporary cavitation pulsation (expansion and collapse) might last for 10 to 12
milliseconds; several pulsations of similar duration will follow. The tissue will still be
moving from the temporary cavitation caused by the first round when it is subjected to the
second temporary cavity, and so on for the third. Will the effect be simply additive, like
three separate shots? Or will the close time proximity cause a synergistic effect,
resulting in a wound that many will call "inhumane"?
This author would like to see some rational testing of
effects (in which the entire projectile-tissue interaction is captured -- not just the
first 15cm) as a basis for estimating wounding effects so that the combat surgeon can be
forewarned and not, as occurs in practice, have to use the wounded combatant to learn how
best to treat some new, unusual wound.
NOTE: This document was edited by TTK Ciar on 2015-05-19 to fix formatting and OCR errors, fill out illustration captions, and anchor tags to illustrations. The original document is preserved here: paper.x.small-arms.wounding-ballistics.patterns_of_military_rifle_bullets.fackler.unk.orig.html
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