Mic. I know people who shoot 40 pounds with spitfires that work great. Just dont panic when you shot something and when you find your arrow the blades are closed. I shoot 70 pounds and the first time I killed something the blades were closed after exit. The explaination I recieved was this.....The arrow slows drasticly as the vanes reach the skin. That slowing causes the blades to return to closed. Made sense to me. Good luck.