Burning propellant ejected
This was the upper stage of the two stage Estes Checkmate. The booster was perfect but as soon as the booster ignited the sustainer, the A10-3T in the sustainer popped and there were bits flying everywhere. My family members said that they say flaming bits bolt out of the rocket body. The streamer was shredded which is a feat as it was mylar. Not burned, but shredded like the engine went forward and exited out of the top. The body of the rocket is creased, wrinkled and blistered. It is soft so it seems to have been burned from the inside. The motor itself is blacker inside than other spent motors and is completely empty. I know it should not have anything in it after use, but I usually don't see them this "clean" (other than the black color).
The rocket is damaged beyond repair.