Airsoft grenades that dont used explosives, Vinegar or baking soda, or balloons filled with water and bbs?
Sorry about the pickiness of the nade but i dont have access to that stuff and Balloons just dont work ( unless if u can find a good idea of how to use balloon nades).
if you have fairly wide springs, pour airsoft pellets into a film can. then, jam a spring into the can, push it down really hard, and throw it. use a fairly weak spring though.
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.
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http://www.maapr.com/phpbb2/viewtopic.php?t=11061
http://www.instructables.com/id/How-to-make-a-cheap-airsoft-Madbull-grenade/
http://shop.ehobbyasia.com/other-gun/other-rifle/snicker-360-gas-powered-mkii-grenade.html