Don't care if it's the same gun or two different guns, or the same volume of powder or not. So long as we're talking the same bullet the only way the energy could be different would be that the velocity is different.

So the guessing game is which powder of equal volume charges is going to yield the highest velocity.

I'm guessing that if it's a light weight bullet, Triple Seven wins the velocity and energy race. If it's a heavy weight bullet, Blackhorn wins. Then again, if the bullet fit to the bore is a bit on the loose side Triple Seven will likely win regardless of bullet weight.