Starman,
Your results are classic "examples of one," and are flawed in other ways, since obviously original bullet weight and muzzle velocity were not the same.
Repeated bullet tests repeated in various kinds of media (including animals), using bullets bullets of equal original weight at a wide variety of velocities, show that frontal area of the mushroom affects penetration as much or more than retained weight. This is especially applicable at higher muzzle velocities.
