Beat P. Kneubuehl, Dr. sc. forens., M. in Math.
Defence Technology Agency, FA 26, Ballistics and Detonics Lab, CH-3602 Thun
In the science of wound ballistics today two general fields can be observed: One concentrates on the bullet-body interaction and the biomechanical wounding mechanism, the other on the medico-biological effects of a gun shot wound or impact.
During the last ten years the experimental possibilities in the first of the mentioned fields have made a big leap ahead. On the one hand tissue simulants for biological structures other than soft tissue have been evaluated as e.g. for bones and skin. On the other hand, in the same period, the technology of high-speed cameras has made an extensive progress.
Both facts allow to simulate experimentally the bullet-body interaction and to study systematically the phenomenology of gun shot effects on the human body.
The physical point of view in wound ballistics concerns in first line the motion of the bullet, its velocity drop and its deformation behaviour and the energy transfer to the body. A second point to look on are the biomechanical aspects of bones, vessels etc. when hit by a bullet or influenced by a bullet passing nearby.
In other words, physical wound ballistics is the aspect of the immediate action. The main problem is to locate and quantify the damage potential (kinetic energy transfer) along the bullet track inside the human body.
Medico-biological aspects deal with the reaction of the body to the energy transfer and the induced shock motion and shock wave through the tissue. The main problem is to determine the tissue damage caused by the damage potential of the bullet and the reaction of the human body.The following comments concern the physical as well as the biomechanical branch of wound ballistics.
3 Simulation Principles
In simulation processes it is essential that physical properties and quantities we decide on are close to reality. In the physical wound ballistics we look primarily on the energy transfer from the bullet to the body. Thus, in a tissue simulant we expect a very similar decrease of the energy of the bullet in dependence on its path. A similar course of energy is equivalent to a similar damage potential at the same location as in a real wound channel.
Good indications for an alike energy course in both, tissue simulant as well as real tissue, is given by the shape of bullets of the same type after penetration. Comparable shapes and about the same penetration depth of both bullets means that the force acting between tissue and bullet had been of the same amount. Since force and path are quite similar, the energy release must be similar too.Muscles and other soft tissue (except the lung) can excellently be simulated by a special glycerine soap or by gelatine of a certain stiffness. Lung tissue can probably be simulated by gelatine with inclusion of bubbles. But this combination is not yet tested.
For the simulation of bones we have taken polyurethane (PU), the same material which is used for the training bones for surgeons. (It is possible to order any bone of the skeleton.) Any of this artificial bones of the skeleton are available. However, for doing reproducible experiments, we recommend to take geometrical shapes, as for example tubes of divers wall thickness for long bones and spheres for the skull. It is also important to simulate the periosteum with a thin layer of latex on the surface of the synthetic bone.
Several samples of synthetic skin and vessels are in evaluation, too.For the experiments bones and vessels are embedded in blocks of gelatine. This allows us to take high-speed-pictures for studying the penetration process.
Experimental simulation with tissue simulant involves several advantages: The experiments are reproducible as often as we need it, we can focus upon the main process, we can do motion studies with high-speed-cameras and, last but not least, by using simulant materials, we do not have any ethical problems.
For each simulation procedure it is very important to validate the simulated results. In the field of the physical wound ballistics an excellent validation method is to compare the results with real cases as for example in war surgery, in legal medicine or in forensic affairs.
4 Simulation Activities
Using simulation material we are able to investigate a lot of interactions between a simulated human body and mechanical impacts. Up to now tests concerning penetration processes have been performed with projectiles and jets, and blunt impacts have been tested with tools or in case of impact deformations behind armour.
5 ApplicationsThere exist three typical applications for the results of the research in experimental physical wound ballistics:
- In the war surgery, it is important to have knowledge of the possible wound tracks and the possible damage potential of bullets and fragments. This allows to make correct diagnosis.
- Very important and suitable fields for the application of experimental simulation are the legal medicine and the forensic science. The simulation techniques using tissue simulants can be very useful in crime reconstruction and in the determination of the applied energy in blunt force attacks.
- The possibility of measuring the wounding potential of a bullet or a fragment gives the possibility to improve the formulations in the International Law concerning the use of small arms in armed conflicts.
6.1 Modelling penetration processes
An actual application of the experimental simulation was the investigation of the wounding potential of a newly developed police ammunition in comparison to the conventional one. We did evaluate not only the energy deposit in soft tissue, but also the effects on bones and on blood vessels. In this context we searched for the distance a bullet can pass nearby a vessel with the result that the vessel still breaks. We made the experience that handgun bullets break vessels only if they have direct contact. Thus the damage radius of a bullet increases only with the diameter of its deformation, and the difference in the damage potential between a classical full metal jacketed bullet and a moderately expanded bullet is not high.
In several cases of crimes we were able to reconstruct the shot dynamic and the wounding effects which was an essential step to the solution of the crime.
6.2 Modelling blunt impacts
An interesting question for a wearer of body armour concerns the damage he will get behind the armour in case of non penetration. In this case one of the most exposed part of the human body is the spinal column. The question reads as follows: Can the spinal chord be harmed by the blunt trauma induced by a bullet which has been stopped in the body armour?
To answer this question we put parts of synthetic spinal columns (with and without ribs) in blocks of gelatine. Then we protected the block with body armours class 1 and class 2. Body armour class 1 was shot by 9 mm Luger FMJ bullet (mass 8 g, impact velocity about 385 m/s) and body armour class 2 was shot by 44 Rem. Mag. SJ bullet (mass 11.7 g, impact velocity about 470 m/s).
The 44 Rem. Mag. shot with the class 2 hard plate body armour gave much less damage than the 9 mm Luger class 1 soft body armour. Behind this soft body armour we did not only find fractures of the spinous process, but also of the lamina of vertebral arch and the transvers process. Fractures of the spinous process are not problematic. However, fractures of the lamina could be dangerous, as small bone fragments could move to the spinal cord.
Since we do (fortunately) not know such a case in reality, we have not validated these results yet.