Rocket Dart Idea

We have been looking at the Water Rocket Index and they have made a rocket/dart that is powered up to high speed using an ordinary water rocket (22mm nozzle for high speed) and then the dart coasts the rest of the flight. The dart is not pressurise but it is quite heavy, so it will carry a lot of inertia. The Water Rocket Index haven't put a payload on their dart but we thought that we could attach our altimeter on it and then make some kind of recovery system. They estimated theirs to reach 400ft at 100psi so we would like to run a couple of tests with this dart idea.

For more info, here is a link to their page:

http://ourworld.compuserve.com/homepages/pagrosse/h2oRocketRb.htm