If you followed the rules of 5gr./pound, I just don't understand how their arrows can overcome the laws of physics.
They don't.
HCA claims one of their bows is safe to shoot with arrow weights down to 3 grains per pound. If you look at their propaganda about their carbon revolution arrows, a chart showing the comparison between their arrows and other carbon arrow brands and models, they show hitting 342 fps with a 250 grain arrow from a 70 pound bow.
That's just under 3.6 grains per pound. That's too dang close to a dryfire for my blood. I'd be flinching like a sonuvagun every time I shot that thing!