One of the defining characteristics of the ongoing protests in Chile has been the sheer volume of gunfire on the streets. Low private firearm ownership and stringent licensing means nearly 100% of the shots fired have come from the Carabineros (gendarmerie) or the military. On November 3rd, the Chilean Red Cross declared that over 2,500 people had been wounded in the course of the protests, at least 800 injured from gunfire. The overwhelming majority of rounds fired are “less-than-lethal” munitions, above all shotgun cartridges loaded with so-called <<perdigones de goma>> (“rubber shot”).
However, it is still far from clear exactly what munitions are being used by the Carabineros. The bloody injuries I have seen with my own two eyes do not correspond to injuries that should result from purely rubber pellets. Others have taken notice, and led to a report issued by researchers from my alma mater that determined the “rubber shot” used by the Carabineros contained no more than 20% rubber, the remaining 80% being composed of a mixture of barium sulfate, silica, and lead. This result was immediately disputed by the Carabineros, who claimed the shot was composed solely of “non-lethal rubber.”
The topic is of great concern due to the high number of face and eye injuries by “rubber shot.” Almost three weeks ago the Medical College of Chile was sounding the alarm over the abnormally high incidence of severe eye injuries due to ballistic impacts from “rubber shot,” which at the time of writing has exceeded 230 and is likely to climb. As a means of comparison, Chile exceeded half the number of recorded eye injuries by less-than-lethal weaponry over the past 27 years in just two weeks, and is on track to match eye injuries made by lethal projectiles (birdshot) in Jammu & Kashmir. The high instance of ocular injuries played a large part in the UN’s condemnation of “excessive force” used on protestors, as well as their calls for an end to the use of less-lethal munitions.
So what’s going on here?
Here I’ll address the topic of “non-lethal shot” used to suppress dissent in Chile, focusing on information publicly available and a physics-based approach to reconcile the issue of ammunition versus injuries. I want to address two issues here. First, exactly what are the police shooting? And second, did they even know what they were shooting to begin with?
Blue shells: chasing down the ammunition used to suppress the protests
Law enforcement in Chile is principally carried out by the Carabineros, Chile’s national paramilitary police force. They are faced with the exceedingly difficult task of managing tremendously popular protests on a massive scale. While many roads forward are possible, the Carabineros have consistently opted for what is called in Chile the “mano dura,” or iron fist. A tactic frequently seen (and heard) is the use of firearms—specifically shotguns—for crowd dispersal.
Exactly what ammunition is used has been a mystery to me. In the United States, police use a variety of less-than-lethal weapons—including tasers, beanbag/”flexible baton” rounds, rubber/plastic bullets, and pepper spray—but never have I seen or heard of the use of “rubber shot.” It is a somewhat ambiguous term, as well—”rubber bullets” and “rubber shot” are frequently heard in reference to the Israel-Palestine conflict, where the term actually refers to metal projectiles with a thin coating of rubber. I wanted to know more.
A common sight on the streets following police action are discarded shotgun shells, usually blue, and bearing the mark of a Chilean company known as TEC Harseim, a Chilean arms dealer specializing in ammunition and sporting firearms.
The “blue shells” correspond to “anti-disturbance” rounds sold under license by TEC Harseim. The rounds do not appear in TEC Harseim’s 2019 catalog but appear in the 2018 catalog (p. 8), where it is stated that each shell contains 12 “postas de goma” (rubber pellets) with a diameter of 8 mm and a rated muzzle velocity of 270 meters per second (885 fps). A third-party website selling these rounds gives information in accord with the information provided by TEC Harseim’s catalog; notably, one website advertising these rounds characterizes the rubber pellets as being “hardened with lead oxide.”
Rudimentary calculations show the pellets cannot be pure rubber
Publicly-available information gives us some crucial information by which a rudimentary ballistic analysis may be conducted. “Anti-disturbance” rounds in documented use correspond to 12-gauge shotgun shells carrying a load of 12 “rubber” 8mm-diameter pellets with a muzzle velocity of 270 meters per second. These data will serve as a basis for the calculations that follow.
The Carabineros claim that the rubber pellets fired are solely rubber. An easy way to check this is to consider the mass of the individual pellets. Although TEC Harseim’s catalog does not indicate the mass of each individual pellet, we can calculate the predicted mass of each pellet based on the diameter of each pellet (8 mm) and a conservative assumed density of rubber of 1.3 g cm-3 (density of polychloroprene rubber). Using the formula for volume of a sphere:
V = (4/3) × pi × (0.4 cm)3
V = 0.268 cm3
We can use the density of rubber to calculate the theoretical mass of each pellet, assuming they are made of 100% rubber:
mrubber = (0.268 cm3) × (1.3 g cm-3)
mrubber = 0.348 grams
According to the aforementioned study (pdf) by the University of Chile, the “rubber” pellets analyzed have a mass of 0.7344 grams, more than double the mass of a pellet consisting solely of rubber. This result suggests the “rubber” shot used for crowd control has been heavily adultered with agents that increase the mass of individual pellets.
The ballistics of “rubber” pellets
It actually makes a lot of sense that rubber pellets have been adultered with mass-increasing agents, as a projectile’s stopping power, range, and accuracy are heavily influenced by the mass of the projectile. Lightweight projectiles are heavily influenced by drag, reducing their effectiveness and accuracy with distance. Imagine throwing a baseball versus a fist-sized wad of paper—although both projectiles may have similar volumes and shapes, the additional mass of the baseball results in a projectile with longer range and terminal energy.
The most basic way of quantifying a projectile’s stopping power is by kinetic energy, which for theoretical rubber pellets leaving the muzzle of a firearm is given by the formula:
KE = (1/2) × (0.348 g) × (270 m s-1)2
KE = 12700 g m2 s-2 = 12.7 J or 9.37 ft-lb
For comparison,
typical plastic pellets
leaving the muzzle carry a kinetic energy of between 0.7-2 ft-lb,
individual birdshot pellets
have approximately 4 ft-lb of energy, and #0 buck (the closest serious munition in diameter) carries about 185 ft-lb of energy per pellet, assuming a 37 g load and a muzzle velocity of 400 m s
-1
.
Using the data from the University of Chile study (mass = 0.7344 g), the kinetic muzzle energy of the adultered pellets is 19.7 ft-lbs, or double that of a true rubber pellet.
These values are under idealized conditions as the rounds leave the muzzle of the firearm; in the real world, effective kinetic energy is influenced by the resistance of the atmosphere (drag). Below I chart changes in the kinetic energy of hypothesized rubber and measured “hardened” rubber pellets with distance. I use parameters (density and diameter) from the pellet measured in the University of Chile study and parameters from hypothesized rubber pellets, both of which are detailed above. Calculations are made per eq. (13) of Allen (2018), which solves for velocity of a small spherical projectile at ballistic velocities over distance; this velocity is used to calculate kinetic energy.
Eq. (13) from Allen (2018). The equation solves for projectile velocity v at a flight distance x. M0 is the muzzle velocity as a Mach number, vs is the speed of sound, x1 is the distance needed for the projectile to drop below Mach 0.7, and kz is a scale factor determined by projectile diameter × pellet density / air density.
Projectile kinetic energy over distance for measured hardened shot (red, solid line) with a density of 2.517 g/cm^3 and hypothesized rubber shot (blue, hatched line) with a density of 1.3 g/cm^3. Decay curves were constructed based on a muzzle velocity of 270 m/s; a pellet diameter of 8 mm; an estimated speed of sound of 34,895 cm/s at 30°C; and an air density of 0.001088 g/cm^3 calculated based on 30°C ambient air temperature, a relative humidity of 20%, a dew point of 4.6°C, and atmospheric pressure of 947.7 hPa, roughly corresponding to “average” atternoon conditions over the last several weeks at Plaza Italia in Santiago (altitude 590 m). Due to the incorporation of these variables, muzzle kinetic energy values here differ slightly than the idealized values presented above. I do not correct for projectile drop, crosswind effects, or interference from the shot cloud.
The casual observer can see there is a significant difference between rubber and “hardened” rubber shot. Namely, the hardened shot is capable of delivering much more kinetic energy to targets farther away. After approximately 25 yards, rubber shot would be roughly equivalent to close-range airsoft pellets in terms of kinetic energy, but the hardened shot would still carry nearly the same (potentially lethal) kinetic energy that the rubber shot possessed leaving the muzzle.
Kinetic energy alone is insufficient to characterize the effects of projectiles on the human body; the sectional area of the projectile plays an important role. Imagine a hypodermic needle—because energy is concentrated on a small area, relatively less energy is needed to puncture the skin than, say, a blunt object. For ballistic projectiles, a value can be defined as the “energy per area of presentation ratio (E/a),” which attempts to quantify the penetrative capability of a projectile as a function of sectional area. Studies have shown that E/a values of 1.3-2 are sufficient to pierce human skin.
I show below the evolution of projectile velocity with increasing distance from the muzzle. Assuming a conservative E/a value of 2, I have also indicated maximum ranges at which both rubber and hardened rubber pellets would be capable of penetrating skin, assuming perfectly rigid projectiles.
Evolution of projectile velocity with distance from the muzzle for measured hardened shot (red, solid line) and hypothesized rubber shot (blue, hatched line) using the aforementioned parameters. Also shown are effective ranges of skin penetration for both hardened and rubber shot, based on projectile velocities needed to achieve an E/a of 2: 164 m/s and 237 m/s, respectively.
E/a is calculated as (mv^2)/(2gπr^2), where m=projectile mass in kg, v=projectile velocity in m/s, g=acceleration due ot gravity in m/s^2, and r=projectile radius in cm; E/a is expressed in m-kg/cm^2. Penetration velocities were back-calculated assuming an E/a of 2 and using projectile weights and radii already established for the hardened and hypothesized rubber shot.
If the Carabineros were truly using unadultered rubber shot, these results suggest skin penetration would only be possible if a target were shot “a quemarropa” (at ‘point-blank’ range, or less than 3 meters from the muzzle of the firearm). Within this distance, the wadding (pellet support, usually plastic) would likely embed itself in skin, which is not to my knowledge common in the majority of hospital cases. On the other hand, hardened rubber shot has the potential to pierce the skin when fired at human targets up to 25 meters away.
I am not even taking into account the “softness” of rubber shot, which by now you should be convinced is not what is being deployed on the streets. Even without considering hardness, it should be clear that true rubber pellets would exhibit very different ballistic characteristics than the hardened “rubber” pellets that are currently being used. It is incredibly difficult to conceive of scenarios in which purely rubber shot could provoke the kinds of injuries being seen in emergency rooms across the country. Rather, the balance of evidence—laboratory analyses, ballistic calculations, ammunition ad copy, and the sheer volume and type of injuries seen—suggests that what has been called “rubber shot” cannot in any meaningful way be described as such.
“Never attribute to malice that which is adequately explained by stupidity”
This is a case where the absolute best scenario for the Carabineros as an institution is that they are deliberately and knowingly promoting the falsehood that their less-than-lethal munitions are composed strictly of rubber. The alternative—given that General-Director Mario Rozas is calling for external testing of their projectiles—is that they actually don’t know the composition nor the ballistic properties of their own ammunition.
Circular Nro. 1.832, issued by General-Director Rozas and which defines guidelines for the “use of force” on the part of the Carabineros, contains a glaring error. In Anexo B, the following definition is given:
“CARTUCHO 12MM. PERDIGÓN DE GOMA: Cartucho calibre 12 mm. el cual mantiene como proyectil 12 postas de goma endurecida, de material de caucho, el cual es de carácter no letal.”
The definition refers to “12 mm cartridges” when the writers assuredly meant 12-gauge cartridges. While both are measures of bore diameter, millimeters are rarely used for shotguns, as bore diameter varies depending on barrel choke and overboring (gauge is instead related to the weight of shot for a particular bore). A “12 mm shotgun” would roughly correspond to a ~40 gauge shotgun, which in any case would not accommodate 12 pellets unless they were much smaller than 8 mm diameter, #4 buck or thereabouts. This is a very, very basic error in an important publication signed by the current head of the Carabineros.
Overall firearms literacy in Chile is low, a byproduct of the extremely stringent gun control laws in effect in the country. One effect is that few law enforcement personnel enter service with prior experience with firearms, and I wonder how much training with shotguns is actually conducted prior to their deployment. I’ve heard from several informal sources the rumor that there must be a secret accord in place wherein the Carabineros deliberately intend to blind and maim with less-than-lethal rounds, as a way of intimidating the populace. I wonder if the quantity of eye injuries could be explained just as easily by poor training and an overall lack of professionalism in dealing with crowds.
Alternatively, if the higher-ups honestly, truly believed that “anti-disturbance” rounds really carried purely rubber bullets, then maybe that would explain the highly liberal use of “rubber” shot to clear protests. After all, the ballistics of actual rubber shot are such that they are unlikely to cause permanent damage when fired from a distance. In the case that Carabineros believed they were shooting little more than up-gunned airsoft rounds that would do no more than sting at a distance, directives to avoid the face and upper body (which do not exist, to my knowledge) wouldn’t be necessary.
This is all a long way of saying that it’s possible the hundreds of people facing long-term injury from less-than-lethal munitions were crippled not by deliberate state action, but rather a failure on the part of the Carabineros to understand and appreciate the tools they chose for themselves. To me, that’s almost worse than ill intent: so many lives altered permanently due to nothing more than avoidable institutional incompetence.
Many thanks to D. Kausel for help researching this post.
EDIT 19 Nov 2300: The Carabineros have suspended the use of “rubber” shot, claiming that the ammunition’s technical specifications were misleading. They literally had no f’ing clue what they were shooting.