I'm not sure if its what your talking about but there is a comparison tool called the Taylor KO factor.So in your comparison of a 270 and 308 if they both are shooting 150gr bullets,with the 270 at 2850fps the TKO is 16.92 and the 308 at 2936fps the TKO is 19.38. Load data taken from the IMR loading data online. I'm not sure what the numbers give you other than a basis for comparison based on the bullet weight, velocity and caliber.