Out by a factor of two, unfortunately....

I went back over my calculations, and the last graphs displayed the volume of 3000 psi air used from the tank.... not the volume of 1500 (average) psi air released by the valve.... Here are the corrected graphs....

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You will note that the volume released per shot at 1.0 FPE/CI is now 1 over 2.5-2.6 of the bore volume.... I added a purple line for the J-P 2:1 ratio, and it works out to about 0.8 FPE/CI when applied to my guns.... My experience tells me that I certainly don't want to release a larger amount of air than that.... The power increase is minimal in the .25 cal, and non-existant in the .22 cal, compared to the amount of air wasted....

I'm not sure about the idea of subtracting 1.0 from the valve volume ratio.... According to some work I've been doing on a spreadsheet, my indications are that if the bore volume is twice the volume released by the valve, the valve closes and simple expansion then occurs after the pellet is half way down the barrel.... I may not have said that properly, but what I'm trying to say is that there is an initial phase during which the valve is open, and then a secondary phase after the valve shuts (in a PCP).... If the volume of air released by the valve is half the bore volume, that inflection in the pressure slope occurs about mid-travel.... If the volume released by the valve equals the bore volume, the valve closes about the time the pellet leaves the barrel.... If the volume released is only 1/10th the bore volume, it closes when the pellet has only travelled about 10% of the barrel length....

This is an over-simplification, I'm sure.... but it allows me to wrap my brain around what is happening inside the barrel.... As you stated, things like transfer port volume.... and the laws of diminishing returns.... will modify the results somewhat....

Regarding the inflection point in the efficiency curve, I've seen that numerous times when you dial the power waayyyyyyy down.... the efficiency rolls over and drops.... It may be friction effects of the pellet in the bore, or the transfer port becoming a significant part of the equation by causing a larger (percentage) of pressure drop in the small charge.... I'm not really concerned about it because in reality I seldom dial a gun down that far.... If I want a very low power, it's better to build with that intent in the first place....

Anyway, have a look at the new graphs.... I'm pretty excited about what I've learned today....

Bob