I would like to be able to determine how hard an impact between 2 entities is. I can tell if they collide with EVENT_ENTITY but not how hard the collision is.

I thought I may be able to use the magnitude of the bounce vector but this always appears to be 0,0,0.

its easy: just look how fast you move your 2 entities just before they collide (with the result-vec or your last speed-vec you could look it up )

I do not think that would work.

If you think of a car driving at 60 mph if it 'clips' an object the impact would not be the same as if it hits it head on.