Semi-computational approach for assessing the damage to human soft tissues: the case of FMJRN versus HP-XTP 9 mm bullet penetration in ballistic soap

Ballistic soap blocks are used in wound ballistics to assess the potential damage of the ammunition employed, allowing observation of the energy transfer occurred along the wound channel. The density and viscosity of ballistic soap (also called tissue simulant) simulate, to a good degree of approximation, the effect resulting from the interaction of penetrating bullets with living human soft tissue. Ballistic soap has a “plastic reaction” to bullet penetration, and therefore, unlike ballistic gelatin, the expansion of temporary cavity remains imprinted in the tissue simulant. When the soap blocks are sectioned or divided with nondestructive instrumental techniques (e.g., Compton’s scattering tomography), it’s possible, therefore, to observe the temporary cavity determined by the penetration of the bullet. This study provides insight into the severity of injuries originated from two different types of bullets of the same caliber by employing ballistic soap as a tissue simulant. In addition, it provides guidance to forensic practitioners on the proper use of ballistic soap for simulating gunshot wounds. The semi-computational approach employed, based on the results obtained from the firing tests, allowed the authors to understand that there is likely a threshold value of projectile energy density, close to 1 J/mm2, beyond which its penetration into the ballistic soap ceases.