Not too many people know this, but the oil refinery near Ventura was shelled by a Japanese sub in the early days of WWII. I wonder if this guy found one of the unexploded shells from the attack, only to have it finally go off in his hand 64 years later?
No, the Japanese fired rounds from a 75 mm deck gun, not a 40 mm. The 5" length mentioned says it was a complete round. Had the teacher found an already fired 40 mm round it would be much shorter.