The force exerted by a spring is expressed as:
where F is the force, x is how far it's stretched and k is the spring rate, or spring constant.
The potential energy of a spring looks suspiciously like the standard Kinetic Energy formula:
Instruments to measure barrel time are pressure/vibration strain gauges. More information about strain gauge instruments, barrel time and links to barrel harmonics and the like can be found here:
Still happily answering to the call-sign Peetza.
The problem, as you so eloquently put it, is choice.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.