More Stable Penetration With A New Solid Bullet
The SuperPenetrator, 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 immediately in an aqueous media (tissue), and would not penetrate sufficient, because the gyroscopic stabilization 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 behavior depends on many factors (material of the target, length 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 1000 fold denser material and the then acting forces.
Few years ago I discussed as an explanation the effect of supercavitation. That means, the bullet is traveling in a surrounding bubble of water vapor 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.
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 stabilization 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 stabilization. In the resin bonded board up to a path of 80 cm no tumbling or other kind of destabilization 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, stabilization 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 important 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 donīt 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 elephant bulls it absolutely sufficient, on elephant cows it smashed additional 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 favor the SP bullet. The entrance holes of the bullets (only a few inches apart on the same elephant 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 bulletīs nose is for its penetration ability. In general, we observe an increasing Penetration in the following order:
- Round nose with semispherical head
- konventional FMJ with a small ogive and flattened nose
- real flat nose bullets*
- bullets with cavitator disk
* 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).
Some FN designs
#1 The original SuperPenetrator, brass, FMJ
and the new Barnes FN banded Solid,
#2 Bridger FN
#3 GSCustom FN Copper monolithics
#4 Speer/Trophy bonded solid. A smaller FN
#5 A new South African Dzombo FN
The ranking of the different nose shapes was shown recently on real game:
"The influence of nose shape of bullets on the penetration in dangerous game". Daniel McCarthy, African Hunter, Vol. 11 No. 1, 2004
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 equivalent is penetrated up to 30 inches.
The image shows the preferred construction, left copper with ogive and steel front disk, length 39 mm. Right bullet is optimized for short length to be used in .458 Lott, lead core, length 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.
How does the SP bullet compare to meplat bullets?
The SuperPenetrator is far more than a wide meplat bullet. So I cannot say too much on this bullet design, but, if constructed properly, it can be the second best design with respect to penetration in game.
Penetration is a very complicated matter and test results are highly dependent on the methodology and the test medium used. The only value of artificial target media such as wood, wet paper, gelatine and others is to compare one bullet to another in that particular medium. Plywood and shooting into baffle boxes has little bearing on penetration in animals.
From the field and test experiments we observed two different mechanisms of penetration in animals:
1. The penetration in aqueous tissue; limited by the stability of the bullets travel in a supercavitation bubble; and
2. The penetration in bone, hide and sinews; limited by the forces acting on the bullet, (friction, shear resistance, viscosity).
Penetration in big game is often limited by the stability of the supercavitation bubble and unexpected bullet paths as reported often in big animals is due to this effect.
It is often supposed that if the base of a solid fishtailed, it hit something and flattened, causing it to bend into a banana shape and therefore deviated off course - missing the vitals. That is incorrect. The process that occurs can be summarized as follows: First the cavitation bubble collapses and the bullet immediately becomes unstable. Due to this instability the bullet then tumbles. This tumbling exposes the bullets side or shank to deforming and/or deviating forces. Now it can be deformed and veer off course. There is not too much to say about the high pressure in front of the bullet, but a FN or the SuperPenetrator causes much more wounding than conventional noses. The pressure cone we can see in shadowgraphs of a bullets flight in air is not existent in aqueous media, because the bullet is travelling with subsonic speed. We observe very low pressure in the cavitation bubble. Not the reduced drag in the cavitation bubble is the most important effect, but the stability against tumbling.
The reduced Ballistic Coefficient in air is minimal and has no practical effect for big game hunting. A not too wide meplat as well as the SP bullet give up roughly 20% of penetration in plywood or bone compared with a Hornady FMJ, but "cannot stopped" in water cans. For animals hunted with bullets of a SD > 0.3 and a muzzle velocity near 2400 f/s this doesn't matter.
The 500 gr Ho FMJ is not stopped in water cans, but becomes unstable and leaves the setup sideways. This was also reported by other authors. I used batteries of up to 20 water cans, 5 liters, each providing 18 cm of bullet path, in total 3.6 meters. This allows to follow the bullets path and its straight penetration with sufficient accuracy. Tumbling is indicated by the holes in the walls of the containers.
You cannot compare penetration in water with penetration in wooden baffles. Remember: We are confronted with two very different mechanics of penetration.
The nose shape of the SP and some FN will be retained in game, wereas other meplat bullets like the GS FN form its meplat by chance under impact and is somewhat sensitive to this. But also the FN or SP bullets, if made from very soft copper, will undergo a compression when hitting very hard bones. This will broaden the nose and reduce the penetration capability.
A wide meplat itself doesn't guarantee a better performance. You have also to look at the other design features. E.g. a meplat formed only by cutting a hemispherical RN shows no effect.
The SuperPenetrator and shot placement on elephant cows.
A test report with images showing the bullet placement and how many shots were needed.
Another theory why bullets fly straight through a medium?
There is no evidence of shoulder stabilization of bullets. All effects observed with bullets in aqueous tissue can be explained without any constraint with the theory of supercavitation as described above.
First it is an erroneous assumption that forces are turning the bullet in tissue around its center of gravity as they do in air. In tissue the center of movement is at the nose, like a top spinning on the ground.
If shoulder stabilized, angular impact should turn the bullet dramatically, but in practical limits, there is no influence of the angle of impact.
Inhomogeneities in the tissue should also turn the bullet, if forces at the shoulder are so effective.
There should not be observed the instability with shots at close ranges. Shoulder stabilization should correct the small angles of yaw immediately.
Shoulder stabilization cannot work with true round noses, but the are flying straight, because they also are stabilized by supercavitation.
For long hunting bullets with a small meplat even the simple model doesnīt make sense: A little shift of the stagnation point will tip the bullet for tumbling.(see fig.) But it shows exceptional straight line penetration.
Shoulder stabilization is possible, when the center of gravitation is close to the front and the object is relative broad with respect to its moving direction and has a short axis. Spacecraft like Apollo are stabilized by this effect, falling leafs and other objects moving in a flow, try to achieve a position where the CoG is near the surface (broadside, not small area ahead.)
Hemispherical RN bullets are stabilized for a shallower penetration depth, because also cavitation occurs, but this is not as stable as with a sharp edged meplat. With shoulder stab. a stabilization should be impossible.
Shoulderstab. is claimed to be effective also in air. I never heard about long hunting bullets stable without gyroscopic stabilization.
And I performed the prove: A near cylindrical bullet with its CoG behind the middle of the longitudinal axis was shot from a barrel without a twist. It was absolutely unstable, it turned immediately after impact 90°, because it missed its gyroscopical stabilization in a cavitation bubble.