[Gunshot injuries of the brain caused by air pressure guns]

Wounding potential of 4.4-mm (.173) caliber steel ball projectiles

From time to time, severe or fatal injuries caused by small caliber air rifle projectiles are seen. In forensic sciences, the theoretical wounding potential of these weapons and projectiles is widely known. Usually, shots against the skull were reported and, in these cases, penetrating the eyes or thin bone layers of the temporal region. Amongst a huge number of different projectiles available for air guns, sub-caliber 4.4-mm (.173) caliber steel ball projectiles were used in an unusual suicide case. This case led to fundamental questions concerning wound ballistics. An 82-year-old man shot once against his right temporal region and twice into his mouth with a 4.5-mm (.177) caliber air rifle. Because of the exceptionally deep penetration of the base of the skull and the use of spherical-shaped sub-caliber air rifle projectiles, terminal ballistic features were analyzed and compared to results published in forensic literature. Test shots using the same weapon and similar projectiles were fired into ballistic gelatin to measure and calculate basic wound ballistic variables of cal. 4.4-mm (.173) steel balls. In comparison, further test shots with cal. 4.5-mm (.177) steel balls BB (ball bearing), flat-headed and pointed air rifle pellets ("diabolos") were carried out. The theoretical penetration depth in solid bone was calculated with 36.4 mm, and test shots in gelatin from hard contact produced an on-average wound track of 120 mm underlining the potential wounding effect. Furthermore, spherical projectiles could roll back and forth within the barrel, and an air cushion between projectile and breechblock can reduce muzzle velocity by more than half, explaining the retained missile in the temporal region.

Energy-dependent expansion of .177 caliber hollow-point air gun projectiles

Amongst hundreds of different projectiles for air guns available on the market, hollow-point air gun pellets are of special interest. These pellets are characterized by a tip or a hollowed-out shape in their tip which, when fired, makes the projectiles expand to an increased diameter upon entering the target medium. This results in an increase in release of energy which, in turn, has the potential to cause more serious injuries than non-hollow-point projectiles. To the best of the authors' knowledge, reliable data on the terminal ballistic features of hollow-point air gun projectiles compared to standard diabolo pellets have not yet been published in the forensic literature. The terminal ballistic performance (energy-dependent expansion and penetration) of four different types of .177 caliber hollow-point pellets discharged at kinetic energy levels from approximately 3 J up to 30 J into water, ordnance gelatin, and ordnance gelatin covered with natural chamois as a skin simulant was the subject of this investigation. Energy-dependent expansion of the tested hollow-point pellets was observed after being shot into all investigated target media. While some hollow-point pellets require a minimum kinetic energy of approximately 10 J for sufficient expansion, there are also hollow-point pellets which expand at kinetic energy levels of less than 5 J. The ratio of expansion (RE, calculated by the cross-sectional area (A) after impact divided by the cross-sectional area (A ₀) of the undeformed pellet) of hollow-point air gun pellets reached values up of to 2.2. The extent of expansion relates to the kinetic energy of the projectile with a peak for pellet expansion at the 15 to 20 J range. To conclude, this work demonstrates that the hollow-point principle, i.e., the design-related enlargement of the projectiles' frontal area upon impact into a medium, does work in air guns as claimed by the manufacturers.

Ballistic parameters of .177 (4.5 mm) caliber plastic-sleeved composite projectiles compared to conventional lead pellets

The capability of conventional air gun lead pellets (diabolo pellets) to cause severe injuries or fatalities even at low kinetic energy levels is well documented in medical literature. Modern composite hunting pellets, usually a metal core (made of steel, lead, zinc, or a zinc and aluminum alloy) encased in a plastic sleeve, are of special forensic and traumatological interest. These projectiles are advertised by the manufacturers to discharge at higher velocities than conventional air gun pellets, thus generating very high tissue-penetrating capabilities. Lack of experimental data on these uncommon air gun projectiles induced this work. Ballistic parameters of 12 different caliber .177 (4.5 mm) composite pellets, discharged from two spring-piston air guns (Weihrauch HW 35, Webley CUB) and three pneumatic air guns (Walther LGR, Walther LG400, Walther LP300), were investigated using a ballistic speed measurement system and compared to a conventional diabolo pellet (RWS Meisterkugel) as reference projectile. Although overall results were inconsistent, for some projectile-weapon combinations (particularly spring-piston air guns), a significant change of the kinetic energy (-53 up to +48 %) to the reference projectile was observed. The data provided in this work may serve as a basis for forensic investigation as well as traumatological diagnosis and treatment of injuries caused by these uncommon projectiles.

Penetrating gunshots to the head and lack of immediate incapacitation. II. Review of case reports

Because of the enhanced intracranial tissue disruption (see companion paper) and the functional significance of the central nervous system, penetrating gunshot wounds of the head commonly result in immediate incapacitation. However, in the last century numerous publications reported sustained capability to act following penetrating gunshot wounds of the head. These are reviewed. A large number of case reports had to be excluded from re-examination because of doubtful capability to act or lack of morphological documentation. There remained 53 case reports from 42 sources for systematic analysis. Favourable conditions for sustained capability to act are present in cases where the additional wounding resulting from the special wound ballistic qualities of the head (see companion paper) are minimized. Thus, more than 70% of the guns used fired slow and lightweight bullets: 6.35 mm Browning, .22 rimfire or extremely ineffective projectiles (ancient, inappropriate or selfmade). A centre-fire rifle or a shotgun from close range were never employed in cases involving intracerebral tracts. A coincidence of several lucky circumstances made sustained capability to act possible in two cases of military centrefire rifle bullets passing longitudinally between the frontal lobes without direct contact with brain tissue. Only two large handguns resulting in intracerebral wounding were used: one firing a .38 special bullet, which solely wounded the base of the right temporal lobe and one firing a .45 lead bullet, which seriously injured the left frontal lobe but whose trajectory was limited to the anterior fossa of the skull. Of the trajectories, 28% were outside the neurocranium. At least 70% of the craniocerebral tracts passed above the anterior fossa of the skull, wounding the frontal parts of the brain. Apart from a neurophysiological approach, this preference can be explained by the fact that the base of the anterior cranial fossa and the sella turcica area serve as a bony barrier protecting the parts of the brain located in its "shadow"' relative to the trajectory against cavitational tissue displacement and associated overpressures. This is particularly true of the brain stem. Intracerebral trajectories not located above the anterior fossa were caused by slow and lightweight bullets preferring one temporal lobe. Additionally, one parietal and one occipital lobe were each injured once by a very ineffective projectile and by a 7.65-mm bullet reduced in velocity. Not a single case of injury to the brain stem, the diencephalon, the cerebellum or major paths of motor conduction and only one grazing shot of the anterior parts of the nucleus caudatus (basal ganglia) were described. Morphological signs of high intracranial pressure peaks (cortical contusion zones, indirect skull fractures, perivascular haemorrhages) and secondary missiles were poorly documented. It is suggested that these findings are at least very rare and not obvious in cases of sustained capability to act.