As I was around 800 yards from the "scene", cannot say what exactly happened. The guy was quite disturbed, so I avoided asking him too much details. Will meet him soon and get his version of happenings.
However, I was told that he was not aware of burst by sound or recoil. And he actually dropped a bird with the last shot, whether it was from right or left barrel is not clear. It was after the last shot he looked at barrel and saw the rupture. It may have happened at 2nd last shot!
I did not realized at the moment to look for empty shell, actually there were lot of these in the boat and it is possible that the said shell may had dropped in water.
