Jason, you are of course correct, the spring is usually a small percentage of the total force holding the valve closed on the seat.... However, it is a much larger percentage of the CLOSING force on the poppet, once the valve is open and flowing air.... If, for example, your poppet has a 1/8" diameter stem, at 2500 psi (to use the same pressure as your example), the closing force on the stem area is only 30 lbs.... A Disco valve spring is 7 lbs on the seat, a bit more (7.5 lbs.? ) when open, so it adds another 25% to the closing force on the poppet during the shot cycle.... Doubling the spring force to 15 lbs would add 50% to the closing force on the stem, or 20% to the total compared to the 7.5 lb. spring.... which will cause an extension to the pressure range that can be used for the same ES.... The spring becomes a larger percentage of the total closing force if you increase it....Mike, you are correct of course, a regulated gun running below the setpoint (unregulated) will have a different curve when off-reg. change if you change the valve spring.... However, it is then no longer regulated, right?.... Sorry I didn't specify a regulated PCP while running above the setpoint, but I though that was implied....Bob