How does the pressure fall before the shot moves? Where does it go? After all, the pressure is created by the additional space that the combustion products need relative to the solid powder. The only way the pressure can fall is if the gases expand, and the only way that gases can expand is if the shot moves.
First & Foremost I did not say the pressure fell before the shot moved, quite the contrary. The only way the pressure can fall is for something to move, or I assume to wait long enough for the heat to dissipate.
Upon the charge moving the volume of the combustion chamber enlarges rapidly. The shot has moved enough for the pressure to have peaked & started falling before the forcing cone comes into play. I can well see the lower compression of the steel compared to lead resulting in a slowing of the pressure fall so that the pressure may remain higher through the cone with steel than with lead, but I do not see it giving an increase in the max peak pressure of the load.
Also, I do not see an increase of pressure being the cause of the bulged chokes with early steel loads. Most users of steel went to larger shot sizes & they simply "Jammed" in the choke reduction & battered the thin walls in that area. Later steel loads use thicker, more compressible walls in their shot cups so that problem has been greatly lessened.
