[sc_rufctr]

Back in the day if there was ever an "unauthorised discharge" the rifle was immediately given to an armourer so he could check the condition of the rifle. If it was found to be faulty the soldier usually got off with a warning but that didn't happen very often. In most cases the soldier was formally charged.

FYI In most cases even dropping a cocked gun wont make it go off.

The big problem with this defence is that any experienced armourer will tell you that guns just don't go off on their own.
To even try something like this as part of his defence is a clear display of arrogance in the extreme!