This rocket was great, although it took my son and I 20 runs to really get the hang of it. We did it for his science project and were able to vary the vinegar 2ml, 4ml up to 10ml while keeping the baking soda fixed at about 1/8tsp (~1/2 base), and found a very linear relationship between horizontal distance and amount of vinegar. We would release the rocket by pushing up with the backs of our thumbs at wait height (3feet), at about 45 degrees. The farthest horizontal distance was 180 feet!
Do not stuff base with baking soda. Gently fill, do not tap it down.
Make sure base is completely dry before putting in baking soda. The baking soda should pour out smoothly of the base.
Getting a feel for how tight to put the rocket on the base takes time.
Shake rocket a few times and give about 10 seconds for everything to react.
Wear goggles, you will get a face full of vinegar.