I built one of these as a kid. I seem to remember it being smaller than 12"...more like 8". I didn't care for the streamer recovery system, so I deleted that and just glued the (balsa) nose cone in place. At apogee, the ejection charge would jettison the motor and the rocket would just come down like a lawn dart. Good times! It had a purple and white or blue and white (can't remember) paint scheme back then, without the huge nose cone. Fins were the same shape.