Jumping around a bit here, since I'm multitasking on a telecon meeting right now, but...on the topic of pressure working against the base of the payload vs. working against the base of the shell/breach: Is there any reason to believe there is any difference in how this accelerates the payload and how/if it is the element that accelerates the shell head/breach aft? I've always believed that the pressure was the force acting in equal but opposite directions, one against the payload and the other against the shell head. Where else would the opposing force act against?