Ping Wyoman- can you help .25 barrel /valve size efficiency

[K.O.]

Hi Wyo

Is it possible to develop a graph for .25  including an 18.75 barrel length like the ones in  building a pumper power plant for .177 and .22

I know I could figure out an algorithm but this is one of my bad weeks for concentration.

Did you just beginning pressure/ ending pressure at 1/3 barrel volume at a given psi(say 1000)  and then keep reducing volume by .05 ?