Shaped charge jet penetration reduction with increasing stand-off

Penetration obtained with shaped charge (SC) jets decreases with increasing stand-off beyond optimum standoff. The common explanation, namely that there is rotation and lateral dispersion of the fragments in the jets, cannot be the reason, at least not for precision shaped charges judging from flash photographs of such jets at stand-off distances that are several times the optimum stand-off. Instead it is suggested that the main reason is that previously eroded jet material in the hole erodes the remaining SC jet fragments on their way to the bottom of the hole. Computer simulation, in which eroded jet and target material are not immediately eliminated once they are eroded, shows that this explanation is qualitatively reasonable. Unfortunately it seems very difficult to design a quantitatively realistic physical model that accounts for this secondary erosion effect due the complicated nature of the interactions in question.