Ballistics ordnance gelatine - How different concentrations, temperatures and curing times affect calibration results

Abstract

A study was undertaken to determine whether different concentrations of ordnance gelatine, water types, temperatures and curing times would have an effect on projectile penetration of a gelatine tissue surrogate. Both Federal Bureau of Investigation (FBI) and North Atlantic Treaty Organization (NATO) specified gelatines were compared against the FBI calibration standard. 10% w/w and 20% w/w concentrations of gelatine with Bloom numbers of 250 and 285 were prepared and cured at variable temperatures (3-20°C) for 21 hours-3 weeks. Each block was shot on four occasions on the same range using steel calibre 4.5 mm BBs fired from a Daisy(®) air rifle at the required standard velocity of 180 ± 4.5 m/s, to ascertain the mean penetration depth. The results showed no significant difference in mean penetration depth using the three different water types (p > 0.05). Temperature changes and curing times did affect penetration depth. At 10°C, mean penetration depth with 20% gelatine 285 Bloom for the two water types tested was 49.7 ± 1.5 mm after 21 h curing time, whereas the same formulation at 20°C using two different water types was 79.1 ± 2.1 mm after 100 h curing time (p < 0.001). Neither of the NATO 20% concentrations of gelatine at 10°C or a 20% concentration of 285 Bloom gelatine at 10°C met the same calibration standard as the FBI recommended 10% formulation at 4°C. A 20% concentration of 285 Bloom at 20°C met the same calibration/penetration criteria as a 10% concentration of 250 Bloom at 4 °C after 100 h of curing, therefore matching the FBI calibration standard for a soft tissue simulant for wound ballistics research. These results demonstrate significant variability in simulant properties. Failure to standardise ballistic simulants may invalidate experimental results.

Keywords: Bloom; Calibration; FBI formulation; NATO formulation; Ordnance gelatine; Penetration depth.