Chuck;
An old set of curves published by DuPont has been posted here on the BBS several times. Admittedly they are of obsolete powders, but show the general characteristics of a shotgun pressure curve. Those curves were run with Black, DuPont Bulk Smokeless, DuPont MX & DuPOnt Oval. All were loaded to a 3 dram or equiv charge with 1¼oz shot. MX showed the highest pressure, then bulk, then 3FG Black & finally Oval (a dense progressive powder intended for heavy charges at high velocity, actually an underload in this case) with the lowest. All pressure curves crossed at approx the end of chamber with the Oval giving the highest out to 10" which was as far as the chart was carried. As by this point the curves had pretty well smoothed out presumably they would retain the same relative position on out to the end of bbl.
It is really rather logical that if two powder charges give the same wt of shot, the same MV but at different max pressures, the low pressure one has to play "Catch-Up" down some portion of the bbl. If the same work is done, then average pressure over the length of the bbl is going to be Essentially equal.
Given the position of the gas port it would seem certain the load with Oval would have operated a gas gun rather more "Smartly" than would the MX load even though the MX had a "Higher Pressure", but remember we are speaking of chamber pressure here. It simply seems that many simply cannot look beyond "Max Chamber Pressure" & base all characteristics of a load solely on that one data point.
