This just isn't possible

[DWTim]

http://www.cnn.com/2006/US/08/30/shell.explosion.ap/index.html

Sendejo told The Bakersfield Californian that he thought the shell was spent and often used it as a "conversation piece." He said the firing pin and bottom shell casing had been removed, along with the gun powder inside.

Sometimes I wish these AP journalists would do five minutes worth of research on the Internet. That sentence is just pitiful... Anyway, I saw and played with lots of inert ordnance when I was a kid. It's pretty easy to determine if it's inert even if not marked so: There's a hole drilled clear through the web so you can acutally see that there's no charge inside. There is no way in heck that what this guy gave the kids was inert, and the author didn't even bother to investigate. I'm leaning toward a HE projectile seated in it, but I have never seen one like that, and it takes a fair amount of force to set it off.

Something amiss here, no?

[muskeg13]

Unfortunately, this is very possible.  A 40mm grenade cartridge consists of a short aluminum cartridge case and the HE grenade.  The 40mm grenade is notorious for producing very unstable and dangerous duds, taking very little disturbance to set them off.  After the grenade cartridge is fired, the cartridge is indeed "spent", but if the grenade didn't go off when it hit the groundor the target, it becomes a very dangerous dud, because the safety and fuze (partially) have already been activated. 

[DWTim]

The article repeatedly uses the term "shell". It never crossed my mind that it could be a grenade. Good point.