Evaluation of the temporary cavity in ordnance gelatine.

Gelatine is a recognized tissue simulant in wound ballistic research. The deceleration of a bullet causes a temporary cavity which provokes radial fissures by stretching the gelatine. The evaluation of gelatine destruction was performed with very different methods yet, widely known are the wound profile by Fackler and the total crack length (TCL) method. Aims of the presented experimental study were to cover a wide range of kinetic bullet energy, to gather all destruction associated parameters and to correlate them to energy dissipation. According to recommendations of the Technical Guideline Commission of the German police and to Fackler, a 10% solution of Gelita Ballistic 3 gelatine was moulded in 20 cm × 20 cm × 50 cm dimensioned blocks. In the front of the blocks a 2 mm thin and 8 cm × 8 cm film bag containing about 8 g pasty acryl paint was integrated. The blocks were cooled to 4°C and were shot from a distance of 5m. The bullet's velocity was measured in front of the target. The expanding bullets Silvertip(®) (Winchester) und First Defense(®) (Magtech) were used. Varying calibres, loads and barrel lengths bullet velocities from 250 to 686 m/s were achieved while kinetic energy was spread from 71 up to 1450 J. All projectiles were captured in gelatine and had mushroomed, as expected. The blocks were freshly cut into 1cm-slices which were optically scanned. The evaluation was performed with AxioVision (Zeiss) software and in each slice the following parameters were taken: longest fissure radius, wound profile (addition of the two longest fissures), sum of the three longest cracks, TCL, perimeter and area of the polygon created by linking the fissure ends. All analyzed parameters - either crack length based methods (wound profile and the TCL) or destruction area based methods (polygon method) - showed a strong dependence of the gelatine destruction and the energy dissipated. This regularity could be approximated by linear function (correlation coefficient>0.95). The gelatine destruction seems to allow a conclusion on the amount of dissipated energy.