Joule creep CAN work in reverse:
Wherein you have a cylinder that's under-volumed to the barrel, a heavier BB would only have pressure behind it for less than the full length of the barrel, resulting in limited acceleration. Whereas a lighter BB would have time to reach the end of the barrel before the air lost pressure.
Or in a system wherein the hopup can't handle heavy weights, forcing the user to crank it up and subsequently losing serious fps on heavy rounds, but being able to run at a minimal loss on lighter rounds.
It's also conceivable in a system with an air leak, whereas a heavier BB results in higher pressure and therefore more leakage.
My point on that was even though joule creep may work in reverse in some cases, it's far less dangerous to be 5-20fps over the fps limit when using .25g or lighter due to the fact it decelerates faster.
So chronoing with heavier ammo controls the more dangerous and common end of the spectrum.
Last edited by ThunderCactus; September 13th, 2014 at 00:36..