Shaped-charge jet penetration of an explosive charge is usually an unsteady process. When the jet first penetrates, the explosive starts to react, and soon the reaction propa gates into the explosive, possibly as a detonation wave. Usually, the detonation wave has a velocity greater than the rate of penetration, and outruns the penetration pro.
Thus, the penetration of our hypothetical shaped charge would be 136.5 millimeters. The above formula only works for very specialized and narrow applications, because it does not take into account material properties other than density which can retard shape charge penetration.
Shaped Charge Theory. A common feature that emerges from these models is the importance of a high strike velocity to exploit more fully the hydrodynamic penetration mechanism, which, in turn, is further improved by the use of longer penetrators having higher densities relative to the target material density. This is amply supported by experimental work.