SOV-4-20 part-1 building and first test flights

The idea:

At the beginning of spring 2011 I found a very thick 0.5 liter bottle, I thought if I could splice a couple of these bottles it would make a great water rocket that could hold up to maybe 200+ psi. The bottles have no straight sides so it wasn't an option to glue the bottles together and I didn't want the disadvantage of airflow restriction with a robinson coupling, so I thought of another way of splicing the bottles. The idea was to cut a hole in the bottom of one bottle, insert a cap in it and put the neck of the next bottle through the hole and secure this with the cap that has a hole in it to let the air pass through.

Building:

I first tested this method with a single splice and it held up to 90 psi, this was the highest I could get with the cheap bicycle pump.

The rocket itself was made out of 4 of these bottles so the total volume would be somewhere around 2 liters. Building the pressure vessel was quite easy but at the first pressure test a problem showed up, when the pressure got higher the rocket started to bend. To solve this problem I added a sleeve over the pressure vessel all the way from the nose to the tail to align the bottles, this solved the bending problem and made the rocket more streamlined but it also made the rocket somewhat heavier then planned. The total weight of the rocket was about 250 grams including the nosecone with parachute and airflap release mechanism. 

The fins of the rocket were made of 2 layers of cardboard glued together and then laminated. I glued the fins directly onto the pressure vessel.

Test flights:

The first test flights were made June 2011 and looked very promising the rocket was tested at a launch pressure of 60 psi, it flew nice and straight without spinning to much. The airflap recovery worked properly releasing the parachute right at apogee, although the parachute failed to fully inflate at the second flight the rocket was slowed down enough to keep the rocket intact. Below is a (shaky) video of the 2 test flights, unfortunately the onboard camera wasn't properly fixed.

Here's another onboard video of a flight that I made a few weeks later. The camera was fixed to the side of the rocket with tape. It was already getting dark so the video is a little underexposed.

Altogether the test flights were a success but would the rocket hold higher pressures...?