An owner of a Vulcan V50 .50 BMG rifle was seriously injured after a round detonated while he was loading it into the gun. The Vulcan V50 is a single shot shell holder. Shell holders are loaded by removing the bolt, inserting a cartridge into the bolt, then inserting both the bolt and cartridge into the chamber. This is normally a very simple, safe and cheap to manufacture action.
When the round detonated, the bolt flew back through his hand, taking off three fingers, and into his shoulder. A friend of his posting on Arfcom wrote that he was initally blinded but has recovered his vision in his right eye and his doctor believes that vision in his left eye may well return. His pinky, ring finger and middle finger were never recovered. The rifle was undamaged.
The ammunition was branded Freedom Arms, but I have not heard of any company going by that name which makes .50 BMG rounds. This leads me to think it was cheap handloaded ammunition. I suspect the cause was a dirty/jammed firing pin. When he slammed the bolt open, the firing pin was pushed into the primer causing the detonation before he had a chance to lock the bolt.
This kind of problem is why I use a Murrays Enhanced Firing Pin on SKS rifles. The SKS design originally called for a spring in the firing pin to push it back, but most manufacturers dropped this to save money. In almost all SKS rifles a firing pin is my floating inside the bolt. A dirty SKS bolt could cause the firing pin to stick out, although this shouldn’t be a problem if you only shoot steel-cased ammunition with military primers and keep your bolt clean.
Many thanks to jdun for the link.