That reminded me of stories I heard about submarine deck guns exploding when the crews didn't allow the water to come out of the barrels first.
Surprised this guy's pistol didn't explode in a similar manner. Maybe he had a cork in the barrel.http://uboat.net/technical/guns.htm
The first time I ever saw a potato gun I was amazed. Made a few of them over the years and used to bring them up to my brother's place when the kids were young. My brother is a steadfast engineering type, always has to overthink everything. Well, one time he had a momentary lapse of judgement and somehow managed to put a water balloon in the barrel of the potato gun. We were firing them with Nair hairspray or WD-40 before they de-atomized the nozzles of the cans.
Well, he fired the gun, and the breech exploded, hitting his hand with pvc shrapnel. Luckily he wasn't hurt bad.