Back in the olden days when I was a kid, we took our empty CO2 cartridges and packed them with match heads and made a cool rocket by dropping them down a metal pipe. The was fun, but we wanted to make it go further. So a little added gunpowder and it went further. Then we put in a bit much. We all looked for it to fly out the end of the pipe and no one saw it go. We looked and looked then we gave up and went to get our pipe. To our horror, we noticed the end of the pipe was much expanded. The good news for us, the pipe contained the explosion, but just barley. We realized it was not a rocket, but a grenade.
We had come within inches of mass injury or death.
We made several great bombs and set them off at Maxwell AFB where we lived. Now days the FBI, CIA, ATF, and likely the CIA would be investigating. Seeing the damage out little gunpowder bombs did to tree stumps and metal cans I honestly can't image a real grenade damage.
I do know if I saw one that had a pin in place the very last thing I would do is pull the pin to see what happens. I would leave the house, and then call the police and the bomb squad.