The standard point for taking the max pressure in a shotgun has for "LOOOONG" years been 1" from the "Breech". The end of a 2 3/4" chamber is 2 3/4" from the "Breech". The pressure point is thus inside the chamber, not beyond it. The above chart was preparred by E I DuPont De Nemours & Co, as best as I recall in the early years of the 1920's, long before Bell was evan a gleam in his father's eyes. The pressure from the 1" point to the 10" point is a decided & distinct "Curve", not a straight line. This is exactly what would be expected from the known characteristics of pressure curves from a propellant. Note also the two popints having the greatest spread occur first at the point of max pressure or just beyond the 1" ppoint & again at about the 4" popint. Also note the order of the various powders are exactly in reverse order at these two points. The curves are all crossing at about the 2½" point.
From this chart it can be seen the danger out where the "Hand" is is totally dependant upon the stated "Honing" of the wall to a too thin condition, but is irrespective of the type powder used. It thus has virtually nothing to do with the smokeless vs black issue as was so often stated for so many years, by those who should have done their home-work as this data was available.
Burrard stated (I believe most of his work was done in the 1930's, with some additions immediately following WWII) that "If" a shotgun bbl burst forward of the chamber or immediately forward of it, the chances of it being from an "Overload" were virtual non-existant. The most probable causes would be an obstruction or faulty metal (which could include being honed too thin).
It is well to note that when Bell did load increasingly heavy loads of "Smokeless" in both a damascus & a steel bbl'd Parker they both burst at very similar pressure (Very Excessive) & both opened up the "Chamber Walls", they didn't burst down where your forward hand holds it.
