Modeling internal ballistics of gas combustion guns.

Potato guns are popular homemade guns which work on the principle of gas combustion. They are usually constructed for recreational rather than criminal purposes. Yet some serious injuries and fatalities due to these guns are reported. As information on the internal ballistics of homemade gas combustion-powered guns is scarce, it is the aim of this work to provide an experimental model of the internal ballistics of these devices and to investigate their basic physical parameters. A gas combustion gun was constructed with a steel tube as the main component. Gas/air mixtures of acetylene, hydrogen, and ethylene were used as propellants for discharging a 46-mm caliber test projectile. Gas pressure in the combustion chamber was captured with a piezoelectric pressure sensor. Projectile velocity was measured with a ballistic speed measurement system. The maximum gas pressure, the maximum rate of pressure rise, the time parameters of the pressure curve, and the velocity and path of the projectile through the barrel as a function of time were determined according to the pressure-time curve. The maximum gas pressure was measured to be between 1.4 bar (ethylene) and 4.5 bar (acetylene). The highest maximum rate of pressure rise was determined for hydrogen at (dp/dt)max = 607 bar/s. The muzzle energy was calculated to be between 67 J (ethylene) and 204 J (acetylene). To conclude, this work provides basic information on the internal ballistics of homemade gas combustion guns. The risk of injury to the operator or bystanders is high, because accidental explosions of the gun due to the high-pressure rise during combustion of the gas/air mixture may occur.

Sturdivan's formula revisited: MRI assessment of anterior chest wall thickness for injury risk prediction of blunt ballistic impact trauma.

BACKGROUND: The thickness and composition of the chest wall are important quantities in multiparametric trauma models for the assessment of injury severity due to blunt ballistic chest impact. While ballistic parameters of non-penetrating projectiles can routinely be measured with high accuracy, data on the thickness of the anterior chest wall is unreliable. Therefore, it is the aim of this work to provide data on the thickness and composition of the anterior chest wall based on MRI examinations of healthy volunteers and to compare these measurements with different empirical estimation rules for the chest wall thickness. METHODS: The study encompassed consecutive male patients from an ongoing population-based cohort study. Each subject underwent standardized whole-body MRI (1.5Tesla). Thickness of total chest wall (CWT) and of adipose tissue (AT) were measured by two independent readers at ten anatomic locations on two cross-sectional planes over the centre of the left ventricle and over the tracheal bifurcation. For each subject, chest wall thickness was estimated based on ten different empirical estimation rules and percent errors were calculated. RESULTS: The study encompassed 250 male volunteers (average age 55.5 years, range 21-84 years, SD 13.6 years). Mean intraclass correlation coefficient of the two readers was 0.90 (range 0.59-1.0, SD 0.08). Average CWT was 31.2mm (range 17.3-51.6mm, SD 5.8mm) while average thickness of AT was 13.1mm (range 3.6-26.7mm, SD 4.6mm). Relative adiposity was 0.41 on average (range 0.19-0.61, SD 0.09). There was significant correlation between CWT and body weight and between CWT and body mass index. Sturdivan's approximation formula showed strong correlation with the measured values (percent error 3.58%, SD 16.26%). CONCLUSION: In this population, Sturdivan's equation formula which is based on the individual's body weight provides valid approximation values for the chest wall thickness and may be used for the optimal design of protective devices and personal body armor as well as for the development of anthropomorphic based test methodologies.