If you want to learn how to make a real grenade, you probably looking in the wrong place, but if you don't mind making an airsoft grenade, you've come to the right place.
Gather up some baking powder, cold water, airsoft BB's, and a film canister and you're ready to build your very own airsoft bomb. This video tutorial shows you just how to do it.
When you're done, all you have to do is shake the cannister up and throw it, then hit the dirt. An explosion of BB's will burst over the countryside, destroying everything in its path.