According to SAMMI pressure standards the 308 cartridge has a max pressure of 62,000 and the 30-06 has a max of 60,000 PSI. Now that is a 3.33% increase to the 308 Winchester. Yes the case is smaller, and therefore more propellant can be placed in the 30-06 case. So, why is the 30-06 pushing on average a bullet of similar weight about 100 to 150 FPS faster?