It happened to me once on a cadet exercise, except it was a oil drum. I had a lump the size of a golf ball on my head for a week!
As for the blank rounds, lets just say the 'jokers' couldn't sit down for a week.
And before i get a Grilled Ass;
I found this in a public domain so this dosen't breach copyright laws etc... and if you don't like this, keep it to yourself!!!