I had this happen to me w/ a 30-06 I was sighting in for a customer when I used to manage an indoor range. I was wearing shooting glasses, and after this case, I don't ever shoot without glasses...period. Anyway, I bore sighted this customer's gun, and then proceeded to the range to put it on paper. The first shot kicked like a mule, and I got sprayed w/ shrapnel. (sp?)
The bolt wouldn't open. We finally managed to bang it open, and found major case head separation. The gun was a bolt action, and I have no idea why we got sprayed but we did. It didn't make sense. I asked the guy what kind of ammo he was using, and he said he reloaded. I asked him what his charge was, and no joke, he said he just filled the case up. I told him he was lucky he didn't kill myself or him. I took his bullets, pulled every one of them and told him to read the Hornady Reloading Manual front to back before he sits at his bench ever again.
On another note, If your friend is using a progressive press, and reloading a lot, it is possible for the powder charge to work loose and spit too much powder. I used to load for the owners of the range on a dillion 1050, (They were ipsc shooters and burned tons of ammo) and I made it a practice to stop after every 100 rds and check the charge. Ocassionaly something would get out of whack (but rarely) and I'd wind up tossing some rounds. Better safe than sorry.
Bottom line...Blown cases can do strange things, and I have not doubt your friend got some brass in him.
VEGETARIAN...old indian word for bad hunter