when it comes to paintball, theres 2 kinds of grenades we use, first is one that is technicly banned in Canada (though its protected by the grandfather law)
it uses a .22 blank and is supposed to work on a 3 - 5 second delay. This grenade was dodgy at best sometimes it had a 10 -20 second delay and sometimes 0 - 1 seconds. They whole bottom half of it explodes out. These ones are not reusable.
The second grenade we use we get from our local airsoft store. Although because of customs they are getting in very low supply of them.
heres a link to a write up