After contact shots to the head biological traces can be found inside firearm barrels. So far silicone coated, gelatin filled box models were used to generate such staining according to the triple contrast method (mixture of acrylic paint, barium sulfate and blood sealed in a thin foil bag). This study was conducted to develop a transparent ballistic model allowing contact shots. Gelatin filled polyethylene bottles with and without a silicone coat were tested in comparison to non-covered gelatin blocks. Finally, thin foil bags of 5 cm × 5 cm dimension were glued on a synthetic absorbent kitchen wipe on top of which 1 L 10% gelatin solution was molded to create blocks of 8.5 cm length. A kitchen wipe with a paint pad on its inside formed the front of the cube. Three contact shots each with a 9 mm Luger pistol and a .38 special revolver were performed on all model variations. The staining was documented by endoscopy and swabs gathered from both ends of the barrel were analyzed by quantitative PCR. Reliable staining was achieved using the front covered gelatin block with comparable results to the silicone coated box model used before. For further research using ballistic models to simulate a human head a symmetric form of the gelatin block such as a cube is recommended.
The powder pocket or soot cavity is a morphologic characteristic of a close contact shot. In a research project concerning staining inside the barrel, the influence of the powder pocket on these traces was investigated.According to the 'triple contrast method', thin pads containing a mixture of acrylic paint, radiocontrast agent and blood were glued on plastic boxes which were coated with a 3-4-mm-thick silicone layer. The containers filled with 10 % ballistic gelatine, were stored for at least 60 h at 4 °C. Thirty-three contact shots were realized using different pistols and 22 lr, .32 auto, .38 special and 9-mm Luger with different barrel length using subsonic, non-deforming ammunition.The documentation comprised endoscopy, high speed video and computer tomography (CT) of the target models. Using image analysis, the ballooning of the silicone coat was studied (lateral view projection).High-speed video confirmed the actual comprehension of the behaviour of muzzle gases in contact shots. The powder cavity rises in about 1.5 to 2 ms, preceding the maximum of the temporary cavity, and the powder pocket's collapse takes 2.5 to 3 ms.The size of the silicone dome increased with decreasing barrel length. Comparing semi-automatic pistols of 4 in. barrel length in the calibres, .32 auto and 9-mm Luger, there were no significant differences of the powder pocket size. Material transport was observed, against and perpendicularly to the shooting direction. CT showed undermining and gas inclusions inside the powder pocket. A correlation between amount and pattern of the staining inside the barrel and the volume of the powder pocket was not observed.
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