It seems to operate on a similar theory as the Lehigh Xtreme Defender, which is a solid copper bullet that looks a lot like a Phillips screwdriver bit. In both, the theory is that the geometry of the bullet uses the rotational force to impart hydrostatic pressure. I remain skeptical of the principle, because the bullets remain at bore size throughout penetration of the target, which means the permanent crush cavity is no different than FMJ. I know the advocates of these types of bullets say the hydrostatic pressure crushes tissue in a wider path than the diameter of the bullet, but all research (and there's been a lot of it conducted by the Army over the years) shows pistol velocity bullets cannot create enough hydrostatic pressure to tear elastic tissue. Rifle rounds are a different story, due to their much higher velocity.
I'm all for innovation though, and maybe they're onto something that will yield results, but me? I'm sticking to Federal HST.
