Guys thanks for the input, been away for a day or so. I'm really suprised the pressure is as low as you say. Only 250 to 500 psi down from 8000. Whats precipitous drop do to, can't just be increase in confinement dimensions by the addition of the barrel volume, is there a temperature drop involved as well as the gas moves down the barrel? Rocketman, I am also interested and will keep looking and let you know if I find anymore info. John C.