The maintenance of law and order and civil peace requires the use of defensive measures by law enforcement officers. Outside these circumstances, in the context of legitimate self-defence, they enable officials to protect themselves and others. It should be noted in passing that self-defence does not only apply to physical attacks, but also to attacks on property and public authority.

The increase in urban violence in general, and against law enforcement officers in particular, calls for an evolution in their means of defense. The switch from the Flash-Ball® defensive bullet launcher (DBL) to the 40-mm launcher is a perfect illustration of the need felt by the administration to equip law enforcement officers with equipment better suited to the assaults they face.

However, it must be borne in mind that the changeover from one DBL to another, more effective one, necessarily involves taking into account the characteristics of the new equipment, checking for possible changes in injury potential and, possibly, defining a new doctrine of use.

Below is an example of a problem concerning the choice of launcher/ammunition pair.

• An example of the DBLs issue. From Flash-Ball^® to 40 mm DBL

To illustrate this, we'll take two DBLs that are well known in France: the Flash-Ball^® from Verney-Carron and a modern 40 mm launcher, but any 40 mm launcher meets military standards and is of good quality. In reality, we're not really interested in the launchers themselves, since it's not the launchers that cause injury, but the ammunition, and in particular the projectiles.

Flash-Ball^®

The two images below show the compact Flash-Ball and the advanced version, the Flash-Ball Super Pro, which have been successively used by law enforcement officers.

Compact Flach-Ball®		Flash-Ball® Super Pro

First, we'll look at the main projectile fired by the Flash-Ball. This is a spherical, honeycombed rubber projectile with an average mass of 29 grams and a diameter of around 44 millimeters. The figure below gives an image of this projectile. A smooth-bore barrel is all you need to launch it. This is the case with all versions of the Flash-Ball.

Flash-Ball projectile

The projectile looks like a small soccer or handball. This is hardly surprising, given that the ball was originally manufactured in China for use in toys. This explains the significant dispersion in mass and diameter measurements on which we deliberately rely.

The ammunition, of relatively complex design, was highly dispersive in terms of velocity, kinetic energy and momentum. Accuracy became uncertain beyond ten meters, virtually prohibiting reliable use beyond this distance. What's more, the projectile, relatively light for its caliber, rapidly lost velocity and, consequently, effectiveness. Nevertheless, the DBL filled an important gap in law enforcement's defensive capabilities. As a means of intermediate force, it was of undeniable operational interest, provided that a serious evaluation enabled a doctrine of use to be defined. Feedback from the field showed that users were satisfied, and that there were few negative consequences when the gun was fired, especially as the short practical distance at which it was used corresponded more closely to the legal framework of legitimate self-defence.

Originally, the projectile's average kinetic energy at five meters was well in excess of the 200 joules stated in the manufacturer's instructions. We were able to measure kinetic energies of up to 300 joules at a distance of 3 meters. Then in charge of the CREL lesion ballistics unit, we conducted lesion ballistics tests with General Jacques BRETEAU of the French Army Health Service. The results obtained led us to recommend a kinetic energy of no more than 150 joules, taking into account standard deviations in speed.

Anecdotally, this 150 joule limit caused a stir among ALR-C manufacturers, who then set the kinetic energy of their projectiles to this value. It had to be pointed out that this 150 joule limit only concerned a projectile with very specific characteristics, and that for different projectiles (shape, mass, density, calibre, hardness) the maximum acceptable kinetic energy on impact could be very different.

Many criticisms can be levelled at the Flash-Ball ammunition and projectile, especially in comparison with the sophisticated ammunition of modern 40 mm DBLs. The projectile's sphericity and lack of rigidity, which are detrimental to good ballistic performance, nonetheless present an advantage in terms of lesions: no matter how many revolutions it makes on its trajectory, the target always receives the same homogeneous sphere. We don't have to worry about projectile stability.

The 40 mm launcher

The image below shows a 40 mm LBD from Brügger & Thomet.

40 mm Brügger & Thomet launcher with EOTech holographic sight

Please note that the above image is for illustrative purposes only. The rest of the text in no way calls into question this launcher, which we had the opportunity to test and which proved to be of remarkable quality. We would like to remind you that we are only interested in ammunition and, above all, its projectile.

The image below shows two projectiles. These two well-designed projectiles have been deliberately chosen. The aim is to demonstrate the importance of adapting the projectile to the launcher and that, for the same launcher, changing ammunition can produce very different results on target.

Two projectiles fired from a 40 mm DBL

The two projectiles shown above are not spherical. They are gyroscopically stabilized and fired from launchers with rifled barrels. They have similarities and differences.

Similarities

Both are inhomogeneous. The body is made of a rigid plastic material, enabling it to respond effectively to the constraints of internal ballistics, in particular the rifling of the barrel, whose truncations are borne by the integral belt. The front is made of a deformable material that acts as a shock absorber. Its purpose is to limit the consequences of impact damage by absorbing part of the kinetic energy.

Differences

The two shock absorbers, which have the same purpose, are different in nature.

The shock absorber of projectile A is made of a relatively dense material, which has the ballistic consequence of placing the projectile's center of gravity GC practically in the middle.

The shock absorber of projectile B is made of a highly honeycombed material, giving it a low density. This explains why the center of gravity of projectile B is positioned far back. Much further rear than that of projectile A.

Projectile A is shorter than projectile B.

Projectile A weighs 60 grams. Projectile B weighs 33 grams.

Even before carrying out tests, we can assume that the stabilization of projectile B will be more delicate than that of projectile A, given the size and low density of the shock absorber, as well as the more rearward position of its center of gravity. What's more, the axial and transverse moments of inertia of projectile B certainly play against its stability.

The tests below confirm our predictions.

Tests and measurements

The shots are fired on ballistic gelatin. The impact zone is protected by poly-aramid folds to prevent destruction of the gelatin. This protection corresponds to a light garment, but has the advantage of not tearing. The two projectiles are subjected to the same experimental conditions, and we obtain the following results.

The two videos below show the shots.

Initial video observations

Projectile A hits the target without any measurable obliquity. The shock absorber is in a position to fulfill its role: to be less aggressive than the rigid plastic body.

The projectile B hits the target with a high degree of obliquity due to a stabilization fault. It tilts as it interacts with the target. A large part of the impact impulse is transmitted to the target by the rigid plastic body. However, the shock absorber, which appears to be more effective than that of projectile A, is not used correctly.

Important note: it would be a mistake to assume that one bullet is good and the other bad. If you look at them, you'll see that they're both well-designed and probably the result of serious research. The only difference is that one is more suited than the other to the launcher that fired it. The use of a different launcher, for example, with a rifled barrel core with a different twist rate, could have reversed the results.

Video measurement results

The two graphs below, Figures 1 and 2, show the loss of velocity of the two projectiles as they interact with the target.

Figure 1		Figure 2

It can be seen that the loss of velocity is greater for projectile B than for projectile A. There are two reasons for this difference: the difference in mass and the fact that projectile B interacts with the target over a larger surface area, as it tilts almost immediately.

These different speed losses give rise to the decelerations shown in the graphs below.

The two graphs below, Figures 3 and 4, show the deceleration of each of the two projectiles as they interact with the target.

Figure 3		Figure 4

The difference in mass between the two projectiles makes it impossible to judge their potential for injury directly from the decelerations. Instead, we use decelerations to assess the forces at play during interaction with the target. It is these forces that generate potential injuries.

The two graphs below, Figures 5 and 6, show a comparison of the decelerations and forces of interaction with the target between projectiles A (blue trace) and B (red trace). While on the graph in figure 5, the deceleration of projectile B is clearly greater than that of projectile A, the graph in figure 6 shows that the force intensities are closer, given the difference in mass: 60 g for projectile A and 33 g for projectile B. Beyond 1000 microseconds (μs), the traces merge, indicating a similar interaction with the target. However, for the same braking force, projectile A will stop over a longer distance due to its higher mass.

The most significant part of the graphs lies in the time interval bounded by t₁ = 0 and t₂= 350 μs. This is the time interval that will be used to compare the two projectiles.

Figure 5		Figure 6

The peak interaction force of projectile B with the target exceeds that of projectile A by more than 20%. Integrating over the interval t₂ - t₁, we see that the mean value of the interaction force is higher for projectile A than for projectile B. This is illustrated in the graphs in figures 7 and 8 below.

The two graphs below, figures 7 and 8, show, over the interval t₂ - t₁, the area of interaction forces (graph 7) and their average (graph 8).

The graph in Fig. 7 shows, for each of the two projectiles, the area under their corresponding track over the time interval t₂ - t₁ = 350 μs. For projectile A :

Figure 7, bleue area

For projectile B :

Figure 7, red area

I_A and I_B, products of a force by a time, are expressed in Newtons x seconds and have the dimension of a quantity of motion. I_A and I_B are often defined as the impulse of the forces F_A and F_B.

For a better comparison, we can reduce the area of the impulses from projectiles A and B to rectangles whose area is calculated over the period t₂ - t₁ from the average braking force evaluated over this same time interval. For each of the two projectiles :

Figure 8

Figure 7		Figure 8

The average impulse due to the force of interaction between projectile A and the target, over the time interval t₂ - t₁, is 30% greater than the impulse of projectile B. There is no proportionality with their respective masses, as the two projectiles impact the target differently due to the high obliquity of projectile B. Projectile A gives up almost 60% of its momentum in the target in the interval t₂ - t₁, while projectile B gives up more than 80%.

Summary of measures

Projectile A :

Weight : 60 g ;

Impact velocity : 82 ms^-1 ;

Impact kinetic energy : 202 J ;

Loss of kinetic energy between 0 et 350 μs : 169 J soit 84 %. Note: some of this energy is absorbed by the projectile, mainly by the shock absorber ;

Impact linear momentum : 4,92 N.s ;

Quantity of linear momentum transmitted to the target between 0 et 350 μs : 2,95 N.s, soit 60 % ;

Average deceleration force between 0 et 350 μs : 8440 N ;

Total stopping time on target : 3900 μs ;

Average deceleration : 21026 ms^-2 sur 3900 μs ;

Average deceleration force on 3900 μs : 1262 N, 2144 times the projectile's weight.

 

Projectile B :

Weight : 33 g ;

Impact velocity : 85 ms^-1 ;

Impact kinetic energy : 119 J ;

Loss of kinetic energy between 0 et 350 μs : 115 J. Note: the shock absorber played its role incorrectly, given the severe obliquity at impact ;

Impact linear momentum : 2,8 N.s ;

Quantity of linear momentum transmitted to the target between 0 et 350 μs : 2,26 N.s, soit 80% ;

Average deceleration force between 0 et 350 μs : 6480 N ;

Total stopping time on target : 2700 μs ;

Average deceleration : 313481 ms^-2 ;

Average deceleration force on 2700 μs : 1039 N, 3210 times the projectile's weight.

Interpretation of results

A comparison of the parameters characterizing the injury potential of a blunt projectile, i.e. kinetic energy and momentum, shows that those of projectile A are higher than those of projectile B. Only the average deceleration of projectile B is higher, which is normal given its lower mass. Only the average deceleration of projectile B is higher, which is to be expected given its lower mass and, having tilted, its larger surface area of interaction with the target. At this stage of our observations, only the instability of the B projectile could pose a problem if it were to hit an area of an individual's body that is poorly protected by clothing. It is difficult to predict the exact nature of the lesions that could be generated in the superficial planes. Nonetheless, there is reason to fear that cutaneous effraction could occur, depending on which part of the projectile's body comes into contact with the skin. In any case, the shock absorber on projectile B does not perform its function, or performs it poorly.

We can also see that projectile A sinks deeper into the target, as shown in the images below. We can therefore expect deeper lesions with this projectile.

Projectile A Depression ≈ 11 cm	Projectile B Depression ≈ 6,5 cm

Important observations: Important observations: the nature of the impulses transmitted to the target by the two projectiles call for two observations:

• The evaluation of the depression depth presents a bias because projectile B tilts. If it arrived at the target with zero obliquity, we can bet that the depth of its penetration would be greater, without however reaching that of projectile A.

• Analysis of the images above, showing the depth of depression, gives an idea of ??the organs which could be affected by this deformation and possibly be subject to damage. The images do not give us any information about how the linear momentum is transmitted beyond the deformation region. Only the inclusion of pressure sensors or accelerometers could provide us with this important data..

• Note that, during mechanical shocks, soft tissues tend to behave like low-pass filters unlike bone tissue which better transmit high frequencies whose impulse generated by projectile B is richer. Keeping in mind that a deceleration of the projectile corresponds to an acceleration of the anatomical planes underlying the impacted region, we can fear that a sudden deceleration like that of projectile B, could be likely to disrupt the functioning of certain organs, such as the heart, without damage being observed (commotio cordis).

Conclusion

The example we have just studied shows the difficulties inherent in choosing an ammunition adapted to a particular DBL. Sometimes market rules lead to having to change ammunition. The consequences can be harmful if we do not pay attention to the adequacy between the weapon and the ammunition.

The transition from a relatively simple launcher, such as the Flash-Ball, to a more sophisticated DBL makes it more difficult to choose the ammunition suited to the weapon. If the best is not always the enemy of the good, it can make the problem more complex. It must be kept in mind that the stability of an DBL projectile goes far beyond purely ballistic considerations but can have direct consequences on its injury potential.

The attitude (obliquity or not) of the projectile at the time of impact can radically change, at the injury level, the consequences of a shot. Note also that a projectile that is intrinsically stable on its trajectory can be destabilized by contact with an obstacle during its flight.

Any modification in the launcher/ammunition pair is likely to have significant consequences.