I recently built a rocket from the Estes Designer's Special kit that was 20.5" BT-60 bodytube long and had a ~35" nylon parachute in it. The rocket has two C motors parallel to each other. Because there are no centering rings for the motors aligned like this, I had to make my own. After I glued in the motor mount, I noticed there was still room where the ejection gases could escape, so I cut out a piece of 1/16th" balsa wood that would fit at the bottom of the rocket to prevent the gases from leaking out at ejection. Well, other day when I launched the rocket, the ejection charge fired, but I noticed that the parachute didn't deploy!! The rocket fell from about 600 ft. and hit the ground pretty hard. Luckly, the only damage was a slightly dented body tube (pics later). I also noticed that the balsa wood at the back didn't do its job with preventing the gases from escaping. The gases made their own way out.....through the back. I don't know if the parachute was too big for the rocket or if the gases escaping didn't deploy the parachute. If anyone has suggestions, please let me know. The RockSim file for this rocket should be included at the bottom.