Using E-25-7 Aerotech ammonium perchlorate core burning motors, single-use. In a light weight rocket, with plastic wings (ali metal was too heavy) and epoxy joints, the impulse of an E-25 can just break the speed of sound at sea level = 760mph. The rocket makes a slight 'crack' sound, unlike the sound it makes in a heavier machine but it is a subtle difference. We couldn't measure the speed for sure - Estimates were using software (speeds were from 1000 - 1500mph). These were built for speed rather than altitude but they still go high. Details in the video. I also made even smaller rocket using these motors using 18mm diameter tubes. These are 24mm. If you do this play safe. Mind you I'm not sure these motors are made in this spec anymore. This video was made a while ago.