First off, What is CE? Did you mean KE? If so most crosssbows have plenty of KE to use a mechanical head. Most will shoot a bolt in the vicinity of 400 grns between 250 and 350 fps, that's plenty of KE for mechanicals.

I would prefer to use a mechanical actually if I was going to use a Xbow. For one fixed blades don't stabilize very well at higher speeds and are harder to tune. Two, you can't really tune an Xbow either like you can a compound bow. So it seems to me a mechanical might be a bit more accurate and forgiving.

Really all they are is a small compound bow mounted on a rail with trigger. The Physics are the same as a bow. They just have higher poundages to make up for the really short power stroke. Most average sized men could get simular performance out of a regular bow if they picked the right one.

Like you said, the only thing I could see that might mess up a Spitfire is how the string is released. I would have to look at one close to see. I just bought my girlfriends dad one for christmas. It was a cheap Barnette though, not a compound one. He just wants to play with it. But I will see how far the string is from the bolt when it is released. I could see if there is some distance between the two and the string slaps into the bolt there might be enough initial shock to open a blade or something. Other than that I would think the spitfires would work great on a crossbow.

Paul