Full credit to GermenWarfare on YouTube
Step 1: Parts List
2 rubber bands, one '3' axle, 4 short pegs, 5 long pegs, 1 weird peice, a three hole technic peice, 2, 5 hole technic peices, 3 'L' shaped peices, and a 2x4 brick.
Step 4: Getting closer...
Step 5: Come on, keep going...
Step 6: Getting closer...
Step 10: Put them like that
Step 12: Put on that pecie
Step 13: Put the rubber bands on like that
Step 14: Pull the top peice under the three hole peice
Step 16: Shooting
put the 2x4 on top of the peice you pulled back,and when you move the 3 hole peice aside it flips up and shoots the 2x4 like 10-15 feet!!!