TexasCHLforum.com

Time for a physics review
https://en.wikipedia.org/wiki/Muzzle_energy

"Although both mass and velocity contribute to the muzzle energy, the muzzle energy is proportional to the mass while proportional to the square of the velocity. The velocity of the bullet is a more important determinant of muzzle energy. For a constant velocity, if the mass is doubled, the energy is doubled; however, for a constant mass, if the velocity is doubled, the muzzle energy increases four times. In the SI system the above Ek will be in unit joule if the mass, m, is in kilogram, and the speed, v, is in metre per second."

This is why an AR-15 shooting a 55 grain bullet produces twice the energy as a 230 grain .45 bullet. (3000 fps vs. 800 fps)