on two pack of motors, clay nozzles were cracked and flaking before flight on all motors in the packs. two failed motors out of two packs(only flew the two). one nozzle lost most of the clay and blew out to about an 8mm hole, the other lost quite a bit of the clay and blew out to a 5mm hole. The first motor sounded like a two stage rocket, it launched off the pad, at about 30 meters in the air, popped out most of the nozzle then rebuilt pressure and continued flying. although at a much lower acceleration.