Always wear safety glasses! A few videos from YouTube illustrate why.
[ Definition: Firing out of battery: when a round is fired before it is fully chambered. Instead of the expanding gas being forced out the barrel it wrecks havoc inside the gun) ]
AR-15 blows up, not sure that happened. Out of battery?
12 Gauge single shot shotgun blows up. A home made shell apparently caused the problem.
He seems to have a problem fully closing or cocking the shotgun. Maybe the shell was to long and it protruded slightly out of the chamber, causing the explosion. Anyone got a better explanation?
The slide is blasted off a blank firing pistol.
A homemade pistol blows up. The barrel shoots off and the shooter gets the steel primer cap embedded in his arm.
AK-47 blowing up. Out of battery. This is an old one I have posted before on the blog.
Safety glasses are your friends. These are WileyX tactical glasses.
UPDATE: A bonus video. The bolt action barrel is plugged causing the barrel to split. [ Thanks to UraniumHead for the link ]