In a conversation (e-mail) which I had with the company that makes the SpitFire, this is what they told me.

In testing, the spitfire would not open earily right up the the speed of 450 fps. That they shot the head out of an air gun to test at the excessive speeds, even tested it frozen in mud, water ect with no failures. The only thing he did caution me on was the retaining clips in the head. That after 5 shots they did start to see the odd failure (early opening). They recomend replacing the clips after 5 shots, but with the praqctice blades, there is really no need to shoot your hunting setup.

Good luck and enjoy.