Excellent, 2-p!! I think we can add more to this model and refine it. Instantanious acceleration will be identical to instantanious pressure. Looking at time-pressure or displacement-pressure curves may give us a clue as to felt recoil. It may happen that we have to average pressure over some short time intervals to account for human reaction. Acceleration from a peak 7000 psi load is less than from a 9000 psi load.