I've seen a few, the first was a home made contraption cobbled together by a friend back in '77, he built a .41 mag out of a .410 shotgun barrel and a home made reciever operated on the zip gun principle, it disintegrated. We found what was left of the barrel, but only pieces of the reciever, which blew out his girl friends car window and very much alarmed the neighbors.
Next was a black powder sixgun that 'roman candled', impressive to say the least. It went up with a tremedous flash/bang series. I've never liked black powder guns and this just reinforeced my aversion to them. Left the shooter bleeding, burnt and dazed.
Next back around '89 or so were 2 M1 carbines that some friends and i had rebarreled into a .17 cal wildcat round based on a .30 carbine, while working up a load the first let go and locked up the action, scared everybody but no blood. We backed down the charge and started up again on the second (of 3 we had rebarreled)things went well untill the action blew and propelled the extrator into the forehead of the shooter. Much blood and consternation resulted. The third rifle still sits in a safe, unfired. No one wanted to be the next biggest fool. This was my one and only venture into wildcatting.
I've also seen the aftermath of a .41 mag with almost a triple charge in a case, did not see it happen but examined the revolver. Top 3 chambers sheared off, top strap bent up and out almost to the point of near failure to hold together and the forcing cone/frame area cracked so badly the only thing holding the barrel in was the pin, the shooter did not get hurt at all and actually did not even realize what had happened untill he tried cocking the hammer back for the second shot. When it wouldn't budge is when he realized what had happend. If memory serves he was trying to load 7g of powder and had set his scale to 17g, we pulled the bullets from the 3 remaining rounds and that was the weight. He later blew up a 1911, reason unknown and took a splintered pair of stocks imbedded in his hands to the ER for removal. He sold all his reloading equipment shortly thereafter.
Lessons learned from the above.
RD