2525,
It is a common misconception that the mere increase in bore volume versus the amount of gas is the total cause the curve drop off.
But why does it drop off so quickly? If mere bore volume was the answer the curve would drop more gradually, instead of at a definite peak. The peak (or just past it) is where powder has ceased to burn to any significant extent.
Last edited by Mule Deer; 09/25/09.
