I keep reading that my crossbow that shoots a 400grain bolt at 245fps is barley enough to kill a whitetail? How is that possible when my 45lb bear Montana longbow easily takes whitetail out to 30 yards with the same weight arrow and half the energy. The website said the short stoke gives it less energy than a vertical bow even though mathematically stroke does not determine for, kenetic energy or momentum of an object. Can someone clear this up to me?