Finding collision force not working in certain situations.

The common answer for finding collision force, as I have read on forums and answers is to get the dot product of the collision normal and the relative velocity, multiplied by the other rigidbody's mass. While this usually works well, it does not produce good results if the object hits sharp corners head on; instead, the normal is just a seemingly random one of the two sides it hit, making the force seem lower. This could be fixed by rounding all corners in my collision mesh, but that should be a last resort. How can I produce better results?