Fill ping-pong ball with high grade black powder. Wrap aluminum foil around it and fill the space in between with bbs. Insert fuse into ping pong ball. B00M careful tho this is explosive..
This one is very good, even though it's not really a grenade. No messy chemicals, fireworks, or ballons. Reloadable mid battle!costs about $1 for every one you make.https://www.instructables.com/id/How-to-make-a-cheap-airsoft-Madbull-grenade/
Get a empty pop bottle. Then fill it with around a 3rd of the bottle with vintager. Next put whatever amount of bb's in it. The get a square piece of toilet paper and put baking soda in it and roll it up. when you are ready to open the cap, put in the baking soda, put back on the cap, sake the bottle until it is really hard. Then throw it and it should explode on impact.
you can get the bottom half of an easter egg and make a little hole to put the wick of a firecracker and fill with bbs and put tape over the top.
try here http://www.youtube.com/watch?v=13JVgEyZycQ&feature=related