I did have a cook off once after a 300 or so round (likely more)slug fest.
I couldn't with all honesty say that it was a cook off or malfunction since it was the middle of a bright sunny summer day and therefor couldn't see if the barrel was indeed cherry red.
However, the targets were becoming very blurred due to barrel heat which also scorched a picnic table that it was set down on. Not to mention that my Hogue forend also melted a bit and deformed/expanded to the point that I simply bought a new one.
All in all, was a fun day!
PS: when shotgunning, I wear gloves