I was not implying that the SRB were end burners. I stated that smaller airborne rockets were end burners.
The “O” rings were never designed to contain a flame front. If the temperature were that high the”O” rings would fail even if they were not compromised.
I can’t say that the SRB had controlled cut-off panels but most rockets that must cut off at a specific point have blowout panels at the pointy end. When these panels are opened the internal pressure is vented and the panels may also act as retro rockets both slowing the rocket motor and at the same time deflecting the motor away from the main stage.
