A target is a target and yes all mechanicals open on a target. However, an animal has flesh and YES, I too have used the Spitfires and had an instance last year that the head didn't open on Flesh.
Those of you that say it's impossible...When I gutted the deer (double lung shot) the markings on the lungs was about a .22 size shot hole with less than 1/8" from the blades sticking out from the top.
I investigated the head and there was no blood, tissue, hair etc anywhere in the grooves the blades sitt in.
FACT!!!