Not sure if this is relevant, but in a gunshop in South Africa, a salesman was repacking 357 ammo when a box went off. Not sure how many cartridges blew, but he had a badly injured hand. I still saw the stiches. I do not remember what make of ammo it was.
Further I was involved in a murder investigations involving a G3 that was blocked for automatic fire. It was essential to establish if the G3 could fire full auto (always two shots) when on single shots. Had used and destroyed (surplus) many G3's but that was the only one with its own will.
On a dirty gun anything is possible, even a firing pin block can be stuck to allow the firing pin to move.
The members here on THR can probably not understand or believe why some people lower/decocking the firing on a loaded chamber of a bolt action rifle, but some fools actually do this. Then the slightest touch on the rear of the bolt will fire the rifle. Such stupidity led to the death of an owner of a 30-06 K-98 Mauser. The question I had to answer was it suicide or accident.
It was a clear case of an accident when the rifle fell over while the gun owner sat on the toilet. The idiot of a judge ruled sucide and the insurance did not pay out.