Penetration of Solids
Do solids tumble in tissue?
Why do solids (nondeforming bullets) penetrate animal tissue and most artificial targets straight to a sufficient extent? In literature we find, following the results of Fackler e.a., the thesis, that all solids must tumble immediatly in an aqueous media (tissue), and would not penetrate sufficient, because the gyroscopic stabilisation in air, caused by the twist, should have no effect in the thousandfold denser tissue. But only solid spitzers in general are unstable in soft media, esp. aqueous tissue, and after travelling a few inches ("narrow channel") they start to tumble. They are not able to generate the stabilizing supercavitation effect (see below) and therefore lacking good penetration. Nevertheless they can show devastating wounding effects and killing power. The actual behaviour depends on many factors (material of the target, lenght of the ogive, shape of the nose etc.). In hard materials (plywood) they can go straight because the tumbling is prevented by forces acting on the shank of the bullet. But nonspitzers, round nose solids and the like are going straight through the target!
The first objective of my experiments was to come up with a sound explanation, based on rules of physics, why solids do not immediately tumble in tissue, as experts in ballistics say they must tumble. They always argue with the 1000fold denser material and the then acting forces.
Few years ago I discussed as an explanation the effect of supercavitation. That means, the bullet is travelling in a surrounding bubble of water vapour generated at its nose. The trick is to surround an object with a renewable envelope of gas so that the liquid wets very little of the body's surface, thereby drastically reducing the viscous drag. The bullet is flying inside a self-generated gas cavity and overcomes the effect of water, that produces 1000 times more drag resistance than air does.
For more information on the fundamentals of supercavitation: click
In general, the idea is to minimize the amount of wetted surface on the body by enclosing it in a low-density gas bubble and to retain the gyroscopic stabilisation.Very important is the gyroscopic stabilisation of the bullet travelling in a supercavitation bubble. Projectiles shot from barrels without a twist are quite unstable within their vapor cavities.
An open question was, which shape of the bullets nose is the best for generating the supercavitation bubble and maximum penetration. There is some discussion on a "cutting edge" to be better than a "pushing or stretching round nose" with respect to effective wounding and on a "shoulder stabilisation" when the bullet tends to tumble. But these theories are not generally well-founded.
Triggered by the disclosure of details of the "Kursk" torpedos, which reportedly also are using supercavitation and some reports from US laboratories, I made some experiments how to improve the supercavitation properties of solids.
Experts believe that the nose of the "Kursk" torpedo features what is likely to be a flat disk with a circular shape. This is the all-important cavitator, which creates the gas cavity in which the object moves. I got some preliminary, but surprising results:
The test setup was a row of thin-walled water containers, up to 12, each about 20 cm length, backed by a couple of resin bonded hard board for recovering the bullet. By checking the holes made by the bullets in the walls of the consecutive containers, it is easy to observe when the bullet starts tumbling and is generating keyholes. Bullets of 500 gr were shot from a .458 Watts/Lott at 2350 f/s. Twist 1:14. Distance 100 yards. The "Super Penetrator" (SP) was used with a layout as described below, the reference was the 500 gr Woodleigh FMJ.
--Shots through the water containers with the SP show a stable flight and a penetration up to more than twofold compared to the FMJ. The FMJ starts tumbling in the 5th container and than mostly leaves the setup. The SP starts tumbling in the 10th container and sometimes did not tumble after a 12th container, depending on the diameter of the cavitator disk.. The tumbling was a 90 degree turn, further penetrating broadside, no deformation of the bullet was observed. Often a change in the direction of flight was observed. The broadside flight is stable, if the gyroscopic stabilisation is no longer active.
--On shots through the resin bonded hard board, which is melting on impact, SP bullets with smaller diameter show a penetration 50 % more than the FMJs, but with increasing diameter, when the penetration in water is increasing, the penetration in the hard board is decreasing.
--Water and aqueous tissue is the most critical issue with respect to stabilisation. In the resin bonded board up to a path of 80 cm no tumbling or other kind of destabilisation was observed. In such materials and probably also in bone the forces acting in front of the center of gravity of the bullet are likely to be compensated by forces working behind the COG, the result is a straight travel through the target.
-- At 20 yards, stabilisation was not sufficient enough for a convincing interpretation. The angle of yaw has to be reached its minimum, the bullet being "asleep". Therefore with close-in finishing shots we often observe tumbling and bullet deformation. Therefore it is advisable to use a twist shorter than the normal 1:14.
The "Super Penetrator", utilizing supercavitation, has the following essential features:
--At the nose a hard, relatively small disk with a sharp, protruding edge (Abreisskante = tear off edge?), where the hydrodynamic flow is converted 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. The greater the diameter, the more stable was the flight through the water. But the penetration in solid media (bone) decreases with the diameter of the disk. A good compromise was 6 to 7.5 mm. The disk was made as an insert from steel in a bullet of copper or machined as an integral part of a monolithic bullet from brass.
--From the nose to the cylindrical shank the head was conical or ogival shaped with a not too big angle off axis. Ogival radius was about 5 calibers. For a conical head an angle of appr. 25° was used.
--The bullet should be launched from a barrel with a twist as short as possible.
Penetration is a very complicated matter and tests are very dependent on the setup and the materials used.
A very inportant fact for maximum penetration in aqueous media (tissue) is also the twist of the barrel. In the water vapour bubble the stabilisation is not as easy as in air. So instead of the 1:14 twist normaly used in .458 calibers it should be replaced by a 1:12 or even 1:10. In the meantime this statement was confirmed by other authors.
Important for close up shots: Bullets must be "asleep". If the angle of yaw (precession) is relatively high near the muzzle, the bullet tends to tumble at impact and is not able to build up a perfect supercavitation bubble. Full stabilisation for a twist of 1:16 or 1:14 is established at about 20 yards. That holds especially for smaller calibers, e.g. some .223 military rounds are stabilized only at about 80 yards. At closer distances they tumble.
I tested the new SP bullet on several elephants with frontal head shots. Penetration and stability was extreme good. But a further comparison to the conventional shape was not possible, because also my 500 gr Woodleigh at 2350 f/s was penetrating as well and all bullets from frontal brain shots were disappearing in the guts. In the stress of a hunt, which had also other objectives, it was not possible to recover the bullets. So, if you have the right cartridge with a penetration index around 120 to 130, you can use any modern solid. The advantage of the SP design is more pronounced, the more aqueous the medium is. With the SP bullet we can find the optimum diameter for the cavitator in relation to the bullets diameter and angle off axis of the head for a given caliber and velocity.
The balance between penetration and shock transfer or energy dissipation on the travel through the animal can also be optimized for the new SP bullet. The edge of the disk generates the supercavitation bubble, its diameter determines the energy transfer and amount of penetration.
It depends on the relative diameter of the meplat (FN area) and the resulting drag function, which bullet is the winner with respect to penetration. But we don´t need penetration much more than 2 meters. A good balance between stable penetration (supercavitation) and pressure wave generation (tissue damage) results in the best bullet for elephant skulls. With this in mind I designed the diameter of the SuperPenetrator for the .458/ 500 grs at 2350 f/s. For frontal head shots on ele bulls it absolutely sufficient, on ele cows it smashed additionel the first vertebra. For maximum penetration and penetration in solid materials I used very different designs. Elephant body shots are already effective with good "softs".
In practice the actual layout of the SP bullet should be useful with cartridges with a low penetration index calculated with A. Alphins formula. Conventional bullets with a PI around 130 have already plenty penetration ability.
New observations hunting plains game with the SP bullets indicate, that they are also very suitable for plains game hunting, they are wounding like softs because they have an enormous pressure generation effect.Also the initial impact mechanism seems to favour the SP bullet. The entrance holes of the bullets (only a few inches apart on the same ele head at the same time) is much smaller for the SP bullet than for the conventional FMJ. Image: left: Hornady FMJ, right: SP bullet. This indicates, that there is a lesser splash as it is with the conventional bullet design.
The actual SP layout is good for raking shots sometimes necessary for back up shots or for shots from stem to stern. For normal broadside shots the trade off should go to less penetration and more energy transfer at shorter paths by increasing the diameter of the cavitator (the flat steel disk).
The design of the SuperPenetrator bullet shows, how important the shape of the bullet´s nose is for its penetration ability. In general, we observe an increasing Penetration in the following order:
*) Nowadays more and more FN bullets are on the market, which feature the improved properties by effects described above with the SuperPenetrator. (Sharpe edged meplat, optimal diameter, nose which on impact forms sharp edges.)
The ranking of the different nose shapes was shown recently on real game:
Image shows bullets from left to right: Round nose; konventional FMJ; Flat nose; SuperPenetrator with steel disk and ogival head; SP with steel disk and conical head; SP from monolithic brass.
Now the SP bullet is optimized for the .458 caliber 500gr at 2350f/s.
It penetrates water soaked paper or water containers in a stable fashion to about 100 inches. Bone equilalent is penetrated up to 30 inches.
The image shows the preferred construction, left copper with ogive and steel front disk, lenght 39 mm. Right bullet is optimized for short lenght to be used in .458 Lott, lead core, lenght 35,5 mm.
Next image shows two designs with conical nose, left copper with steel disk, right integral brass. weight around 440 gr, not further followed.
Next: The 500 gr lead core SP, from left to right: 1): new. 2): recovered from 27 " resin bonded hard board. 3): recovered and stopped by a steel plate after passing in stable flight through 95" of water containers.
For a as short as possible dimension of the bullets head, a special design was found, which consists of a second sharp edge behind the protruding Cavitatordisk:
The SuperPenetrator , the special non deforming
bullet for big game hunting, is now commercial available in Germany. It is
the type from copper monometal with a steel cavitator disk. It shows very
stable penetration in game and no deviation, tumbling, bending or fishtailing
and a up to fourfold penetration length in animals. Only intended for
big game it will fabricated in cal. 9,3mm, .375, .416, .458,