You know what they say about initial reports. We had a very similar incident at Fort Sill many years ago except it was on an 8 inch howitzer and the round exploded in the breech (nobody opened it). It blew the whole tube off the carriage and nobody got killed but a few guys had minor injuries. Hairline crack in the base of the round was determined to be the cause as they found other rounds in that same lot with hairline cracks in their bases.