Instantly upon ignition, the forward motor closure and 3 propellant grains were ejected from the top of the motor. The forward flange that had been rolled into the casing was unrolled, resulting in a flat tube (no longer rolled and able to contain the forward thrust). There was no post incident burning of the ejected grains nor the grains that remained within the casing. It was just like an M80 went off in the motor tube, then nothing but pieces. The rocket and motor were destroyed.
When ignition occurred, the incident was over instantly.