The purpose of this article is to evaluate an equivalent projectile giving the same effects as the Back Face Deformation (BFD) of a helmet impacted by bullet.

Several tests are presented to evaluate the Behind Head Blunt Trauma (BHBT). First results on a classical aramid helmet are developed against 9mm bullet (NIJ01.0104 Level IIIA). Two kind of measurements are exploited: deformation of a clay head form using plastilina Herbin Sueur and a head surrogate with force sensors developed by BioKinetics (BLSH). Those results permit to give the Blunt Criteria (BC), and the AIS score, for the scenario of impact. In a second time, some equivalent projectiles are used against plastilina Herbin Sueur and the BLSH and compare to the realistic shots on helmet.