LB,
My take on Don's point was that pressure is distributed equally in the available volume at any instantaneous point in time during the acceleration of the payload. So, if you measured strain/pressure 1" from the breach, at a particular time in the firing process, the pressure would be the same at that time from the breach to the point just behind the wad base. If a payload was halfway down the barrel, the pressure behind the way would be the same as at the breach, at that particular time. There may be some gas dynamics that aren't accounted for in this conclusion, but it should be reasonably close. The Pressure Trace will, with a single measurement point at the breach, measures pressures for the entire trip of the payload down the barrel. It is depicted in a pressure/time curve. Figuring out exactly where the payload is along the barrel is tougher. Bell's setup of testing at ports along the barrel eliminated the job of figuring out where the payload was along the barrel at any given time.
My understanding of Bell's multi-port testing was to see if peak pressure occurred and/or higher pressures were maintained with the payload significantly further down the barrel when using slower powders than with faster powders. This was a theory that, if true, could expose thinner areas of the tapered barrels to higher stress than might be safe. It would not neccesarily have to be peak pressure that ruptures a barrel in the thinner sections further down the barrel. Just pressures that exert higher stress than that section of the barrel can take. I'm guessing we have the same understanding of what Bell was trying to reveal.
