Estes A8-3 Burn Through

After the July 18 launch, I was removing the Estes A8-3 engine from my Squatty Body. Here's what the casing looked like.
To the right (nozzle) side you can see lots of charring and what looks like a hole.



I made a long cut down the length of the casing and unrolled the paper.
It's clearly a burn through.

I've seen this happen in monocopters with Quest Chinese made engines.
This is very unusual on an Estes engine.




Here's the inside of the engine mount showing the burn through hole. It didn't go through the outside body tube so it'll be okay for more flying.

NOTE: Never cut into a live, unused engine!
This expended (used) engine posed no danger when opened up for post-flight analysis.