Brass marking on extraction (and blown primers)

[alamo5000]

Based on that video and the fact that you were shooting heavy bullets for caliber it leads me to think this is probably the most likely cause.

Meaning that chamber might be one of the hybrid type and you were definitely shooting 5.56 brass so the added few thousands on the brass plus the heavy bullet probably caused your problem.

Throw in the chamber dimension and that solves it in my mind.