On another forum i am a member we would call that "EPIC FAIL!"
E=mc2 Einstien wrote.
http://en.wikipedia.org/wiki/Mass–energy_equivalence
On paper it doesnt work exactly as it states with bullets,at least not to me.To get energy you need mass,alot more than you need speed.
If you start ramping speed you get higher E,but with bullets it doesnt have the same effect as ramping the mass.
I finished high school and some EE work,so im not physicist and most likley misspelled it.
The only reason i see to ever go with lower grains on a bullet is to reduce recoil.Reduced recoil with a lighter and faster bullet will give you higher E on paper,but in reality you can even feel its not true since the reduced felt recoil says otherwise.