crossbows are legal in most countries.check out the laws on Wikipedia or Google before proceeding further.All i know its legal in India.also please write in comments below which countries have it legal.
Step 1: Making the Design
Step 2: Making It Real Part One-mechanism
then follow this video to see how to copy final art of design onto it (accuracy required)
then drill and sand it up.
Step 3: Making It Real Part Two-making the Body of the Crossbow
there are three layers of it so get three.
drill them accordingly
join with screws nails and glue as shown in images
Step 4: Making It Real Part Three-making the Pistol Grip
Step 5: Fix a Bow or Rubberband Strip
fire it until its string breaks ones.
then replace the string
Step 6: Fin
now go on a hunt or target practice.