The video won't play on some browsers, but here's a version that will always play.
http://www.youtube.com/watch?v=HEOEu6k6sFE
That was caused by dirt in the barrel. You can see the clump of dirt pop out when the barrel splits. The shooter probably allowed his muzzle to sink into the the soft ground and caused an obstruction which of course lead to catastrophic barrel failure.
Until I saw this video or the pics of the guy that had a similar experience while shooting and forgetting to take his boresighter out of the barrel, I had no idea the gun barrel splits open like it does in old Elmer Fudd cartoons.
