Ahhh... Corey here' s why these forums are such a good thing. You learn something new everyday!

There is a reason why the blades do not open fully on the face of a foam target ,yet they will everytime on a live animal and that has to do with the design itself.
Swing open mechanical heads such as the Rockets require a rearward leveraging force to snap the blades open......to acheive this and to get the blade tips around the outermost radius of the blade arc ,the material shot into needs to be of a flexible nature or have some give.....such as you find in an animals hide with hair and then flexible skin.
When you shoot into a hard foam target the blade tips simply bite and penetrate the face without opening because there is not enough intitial give in the target material to allow the blades to freely swing to the open position. There might be enough friction within the foam taregt itself to get them to force open by the time the reach the backside, but they just won' t open on a flat foam surface.

You want to see this illustrated?......take a deer hide(would be the perfect material), or a sweatshirt or something like that and hang it over your foam target. Now shoot it and you' ll see what I mean.

The exception I have found to this rule is with the NAP Spitfire.......while the basic design is the same as a Rocket head, the nature of the very stiff blade retention clips can and will cause some bullet hole style entrance wounds.