.png)
Bullet Shape
Like the design of supersonic fighter jets, bullet shape will always be a compromise. The optimum wing and fuselage design for a Mach 2+ fighter is old established knowledge but the unavoidable bottom line is that it will spend 90% of its airborne time at subsonic speeds. The very low speed for take-off and landing already determines that a perfect supersonic wing design will stall on getting airborne so we do not see any fighter with true supersonic wing designs.
Similarly, despite a hunting bullet spending 100% of its flight time above Mach 2 the object of its existence is not flight but impacting and penetrating very dense bone and meat to mechanically cut through the animal’s heart and sever the oxygen flow to the brain so that neurological function is lost.
This section is about the special bullet shape needed for special performance. Special performance when killing thick skinned, heavy boned, densely muscled dangerous game relates to penetration through these obstructions - and ONLY that. For the very thick skinned Cape buffalo and elephant the importance of a high BC bullet is so low on the priority scale that it can be ignored. Nobody shoots an elephant or a buffalo or even a giraffe further than 50 yards. Special performance for a special need.
Bullet manufacturers in the USA have for scores of years defined the ”special performance” regime for hunting bullets as their low drag ability in flight. This, by marketing spin has re-actively become the #1 priority for most hunters. In South Africa the highest priority for most hunters is the terminal moment, so their demand on bullet manufacturers is to define the region for special performance as that 1,000th of a second after impact. The same reason why heavier, slower bullets are in demand here.
Bullet design in the USA is manufacturer and marketing-spin driven, while in Africa it is driven by hunter requirements for on-game performance - one shot through the heart killing ability. Bullet manufacturers respond to user demands here or they will go out of business.
The best shapes for lowest aerodynamic drag at supersonic velocity cannot be applied due to the requirements of the special performance demand mentioned above (compare Figure1).
Similarly, the requirements for low drag at subsonic speed that at first sight appears to be better suited to the special performance demand can also not be utilised because the massive supersonic drag on these designs causes unacceptable bullet slow down even in the first 50 yards (see Figure 2). Popular values for ballistic coefficients (BC) - which often do not follow actual supersonic aerodynamic drag principles, -are useless when a DG bullet is designed to meet its post impact special performance demands.
Figure 1. ¾ Parabolic Cone.
This is the best aerodynamic shape for Mach 2 - the speed of a 500 gr .458 Lott at 50 yards. Low shock wave drag is the design driver for the ¾ Parabolic Conical nose section. For in-animal performance no poorer shape can be imagined.
Field experience has long ago showed that a slender nose, also being too long for magazine rifles, gets displaced (yawed) in virtually every instance by bone in buffalo or elephant. The centre of mass of such bullets are also too far to the rear. The biggest flaw of such a design is the massive in-flesh surface friction it experiences due to its into-tissue “creeping” which causes linear and rotational friction, slow-down, and loss of gyroscopic stability, wobble, and low penetration. Furthermore, slender nose shapes are too weak for the impulse counter-force they must endure at impact.
Comparing bullets to jet fighters again: the only advantage this shape has for a Mach 2 jet fighter over a straight-edged cone is the lack of a shock wave where the cone flows into the fuselage; a shock cone here would cause unacceptable conditions for some systems, including the perspex canopy. On a bullet inside an animal with 800x the density of air in such a shock front from a cone shape angular transition from nose cone to shank is very beneficial.
Figure 2. Elliptical.
This nose shape is the best design for lowest drag for velocities below 850 ft/sec. For any hunting bullet it is an aerodynamic drag disaster at supersonic speeds as its critical drag rise Mach is already at M=0.80. Even a flat nose, conical shape has lesser shock wave drag at Mach 2. The velocity degradation on a bullet of such a nose shape is acute during the highest velocity regime which is out to 50 yards from the muzzle.
This shape does put more mass into the front end of the bullet, making it stronger, but the long nose still is its Achilles Heel, so to speak, regarding in-tissue deflection - particularly by bone, causing yaw, followed by wobbling and immediate loss of penetration.
Figure 3. Elliptically blunted cone.
This blunt design was a feature of a Winchester FMJ (nickel coated) in the 1970s. It had stable penetration in soft skinned game due to the almost flat nose but the ogive design still caused it to slip into the animal tissue which caused wound channels of less than calibre size.
This was the start for moving away from aerodynamic performance towards animal tissue performance. It was popular on thin skinned animals like eland due to the low amount of meat damage. It was effective on elephant frontal and side-on brain shots but not on heart shots on either elephant or Cape buffalo.
Figure 4. Power Series.
The midrange shape in the radii indicates the mean compromise between a straight cone and the elliptically blunted cone. It retains the low supersonic drag coefficient of the straight cone while allowing for a blunt nose to create fluid containing tissue to shear ahead of the bullet at the moment of imminent contact, preventing the onset of friction drag on the bullet immediately. This was the start of the cavitation principle.
With a larger blunter nose and therefor flatter conical angle of attack this is close to what the Peregrine VRG-2/3 series have.
Figure 5. Bi-conical.
It was previously stated that a distinct shock front immediately in front of a flat nose bullet creates a tissue shearing action and the start of a cavitation bubble. Another shock front at the transition from nose cone to shank enhances the cavitation bubble and lessens skin friction drag tremendously.
This is an acceptable and cheap rocket design. By removing the frontal cone at Ø1 the start of the perfect bullet for in-animal special performance has begun. As mentioned earlier bullet design is a compromise between aerodynamic and in-animal performance, and for the best performance to kill a Cape buffalo at 40-50 yards aerodynamics must take a back seat.
Figure 9. Super Cavitation.
This concept will immediately be understood by boat owners: when a propeller cavitates in the water the removal of the drag force on the blades cause an immediate and significant increase in rpm (angular velocity). For a bullet inside animal tissue this ability has huge benefits.
Very promising empirical results on elephant have been obtained with this concept in South Africa. The flow separator is a separate disk centered on the mephlat which strengthens a shock front around the body by vapourising any fluid containing tissue. Penetration through tissue and bone is impressive.
The main advantage is preventing friction-creating tissue to be in contact with the bullet shank. Keeping this - what is known in aerodynamic terms as the "wetted area" as small as possible, skin friction drag is limited to the flow separator and penetration is considerably enhanced per impulse force. The flat nose concept of the Peregrine and GS Custom bullets achieve this to a certain extent - not only inside an animal but they also have considerably less aerodynamic drag at Mach 2 than round nose dangerous game bullets.
(Next: Cavitation and Super Cavitation bullets)
Designing The Super Penetrators ©
History
Any non-expanding spitzer bullet, solid or FMJ, will more often than not wobble and even tumble through animal tissue. Depending on variables of sinew and bone in the way even round nose FMJ and solid designs will at times display this phenomenon.
A partly correct explanation was given by Dr. Martin Fackler, a firearms murder forensic expert. Based on his knowledge that body tissue consisting of mostly water and cell membrane is 800x denser than air his observations were presented in a number of reports. A bullet slipping into and amongst the cells of this medium the drag force not only retards the linear velocity but also the angular momentum imparted to it by the rifling. Gyroscopic rigidity is rapidly lost, the bullet becomes unstable resulting in wobbling and even tumbling. Penetration is immediately lost and a nauseatingly loss of good meat will confront the hunter when he eventually finds the animal.
Shooting non-expanding previous generation solid bullets with any nose ogive into a line of twelve 5 litre jugs filled with water demonstrates how wobbling starts almost immediately. Even the Woodleigh FMJ round nose tumbles after the second jug. All the exit and entry holes will show tumbling keyholes.
Then again, shoot the same bullets into dense, solid wood blocks and the straight line penetration inside a calibre diameter wound channel is impressive. This one is easy to explain: Even though the skin friction caused by the wood in contact with the bullet rapidly stops rotation, the solid wood surrounding the bullet shank keeps it straight and the penetration impulse remains centred on the apex of the nose. Relying on a bullet’s penetration into wood is a very sandy foundation to build confidence on for its future stable passage through an animal as has been proved many times over.
Why Fackler’s explanation (and repeated by others after him) is only partly correct is that the conclusion was made that all solid (non-deforming) bullets will lose stability and tumble when entering any viscous medium. For the past 16 years or so South African made solid bullets have been showing impressive stability and penetration through even the heaviest bone and sinew and muscle of elephant and Cape buffalo. So do lighter solid bullets of smaller calibre through other big game and still cause at least 2x calibre wound channels - the same as created by expanding bullets .
The reason is “super cavitation”. This is not a hyped marketing catchphrase but an accurate description of what these bullets do to stay stable, penetrating nose forward all the way.
Consider the phenomenon of wound cavity:
Permanent Wound Cavity
This is created by the mechanical cutting or crushing of tissue as the bullet passes through. Experience shows that bullet velocity has no bearing on the diameter of the permanent wound channel - only the post impact physical form and construction of the bullet has.
Temporary Wound Cavity
According to Fackler, after passage of a bullet, the walls of the permanent cavity are temporarily but radically stretched outwards. Flacker contended that the potential utilisation of this effect depends on the shape and construction of the bullet and its interaction with the tissue. He proposed that the expansion of this “super cavity” occurs milliseconds after the exit wound is created but did not offer any explanation of the mechanisms involved. It is easily explained by the supersonic shock cones around the bullet, dragged along by it and pressurising the passage channel.
My own observations on 7.62x39 wound channels (most smaller than calibre) on soldiers shot in combat confirmed Fackler’s report that the temporary cavity collapses immediately back to the diameter of the permanent cavity. These facts observed particularly by elephant hunters / cullers using .458 Lott ammunition set of new thinking and new research. At about this time the knowledge of the Russian Kursk submarine became known.
Enter A Russian Marine Engineer into South African Hunting Bullet Design
A man who understood that cavitation in water was a good thing for projectile bodies, he designed the Kursk submarine's torpedoes which had their range extended by a factor of almost 2 by a device on the nose which created a real time “super cavitation bubble” around the missile and which removed the drag force of the water from it. Not a post-passage cavitation expansion, but slamming the fluid around the body away in one continuous fell swoop during passage.
A light bulb went on in the minds of a few engineer-hunters in South Africa: “What we need is a real time super cavitation bubble around our bullets to remove viscous drag, maintain spin and stability and increase penetrating range.” By controlling the Mach 2 shock front around the bullet this was achieved. The flat nose bullet was born.
The immediate results::
Group #2 below: Bridger brass flat nose bullets with conical front end and narrow drive bands to minimise barrel friction.
Group #3 left: Peregrine VRG-2 dug from the ground after an insurance brain shot on a downed elephant.
Group #3 right: GS Custom FN removed from an elephant's neck vertebrae after a frontal brain shot.
All these solid bullets conform to the principle of super cavitation. Then a young German engineer-hunter after elephant in Zimbabwe decided that he could improve on that. He wanted the ultimate design for super penetration and started experimenting with the Kursk torpedo frontal disk.
He decided to surround the bullet with a highly enforced (more than the flat nose bullets) continuously renewing envelope of water vapour so that the "wetted area" of the body's surface is only limited to the frontal surface thereby drastically reducing the viscous drag. The bullet must be flying inside a self-generated gas cavity and totally overcome the effect of any viscous matter.
Various designs were made on a lathe and for comparison purposes shot through rows of 5 litre water jugs with a steel plate at the end. Here is his final design which employs all the findings of his long research.
The Super Penetrator (SP) features, quoted from his reports:
A hard metal disk extending sideways with a sharp edge past the mephlat is fitted to the nose of the bullet.
This converts the hydrodynamic flow to a quasi aerodynamic flow. The diameter of the cavitator disk for a .458 (11.63 mm) at 2400 f/s was 5 to 8.5 mm for the tests. The greater the diameter, the more stable was the flight through the water. The penetration in solid media (bone) decreased with the diameter of the disk and a good compromise was 6 to 7.5 mm. The disk was made as a steel insertinto a copper bullet, or machined as an integral part of a monolithic bullet from brass.
Tests firings were from 100 yards using 500gr bullets from a .458 Lott with a 1:14" rifling twist rate, at 2,350 ft/sec. The reference bullet was a 500 gr Woodleigh FMJ.
There was no penetration performance difference between conical and ogive nose shapes of the SP.
In all instances penetration performance was easily a 100% improvement on the round nose Woodleigh FMJ.
Later it was seen that the performance on elephant were equally impressive, duplicating the ratio difference with the Woodleigh.
Here are some of his bullets:
Group #1: the original copper SP on the left, a monolithic brass FN in the centre and the Flat Nose Banded adopted by Barnes on the right - which is a hybrid of the first two designs.
4&5:The South African Dzombo FN on the right, compared to the Speer Trophy bonded FMJ.
Some loaded ammunition for elephant:
From the left:
PMP Brass solid, Woodleigh FMJ, Peregrine VRG-2, SP ogive, SP conical, SP conical brass
Since these it has been strange to see any other bullet than a GS Custom FN or Peregrine VRG-1/2 or a Rhino used on buffalo or elephant.