I have a crossbow that I borrowed from a friend. It's a Barnett Quad 300. Seems like a good enough crossbow, but it shoots WAY high. I've lost a bolt and target point already. I tried putting washers under the front mount, as you can see in the picture.

http://www.the-hartmans.org/xfer/2009-03-18_scope.jpg

I have NO idea what the problem would be or what steps to take. No amount of dialing in the adjustments seems to help. I'd appreciate whatever guidance you can offer.