Ballistic gelatine—what we see and what we get

Abstract

Since decades, 10% gelatine is used to visualize and estimate the energy transfer of projectiles. The study performed investigates the correlation of the temporary cavity (TC) recorded by high-speed video (HSV) and the cracks in gelatine slices. A total of 36 shots were performed from distance using form-stable bullets (FMJ), 12 using deforming bullets (HP) in the calibres .32 auto, .38 special and 9 mm Luger. The target models were prepared according to Fackler’s standard as 10% gelatine cubes with 12 cm edge length doped with a paint pad beneath the front cover (“reference cube”). Scaled images of the TC were recorded with 40.000 fps. The cubes were cut into 1-cm-thick gelatine cross sections, which were scanned. The evaluation of the destruction (cracks) was performed by the mean of image analysis measuring the longest crack, the wound profile according to Fackler and applying the polygon method. The height of the TC was measured each cm along the bullet path. The energy deposited ranged between 54 and 269 J. FMJ caused tubular, HP provoked pear-like TC. The tubular aspect was consistent with the quasi-constant deceleration of FMJ; however, the pear-like TC did not metrically represent the deceleration of HP. The profiles of destruction parameters were convex for both projectile types and did not match the profile of bullet deceleration. The maximum of TC stretching observed in HSV did not coincide with maximum gelatine destruction (crack lengths). The total energy transfer correlated with all considered destruction parameters in their sum; however, the cross-sectional parameters did not reflect the energy transfer per centimetre bullet path. The sum of the TC’s heights correlated with the energy deposited, but differently for FMJ and HP. Obviously, the 12-cm reference cube reflects the energy transfer by a bullet as a whole.