The guys at MilSim Labs have some details of their Mark 3 Airsoft BB Grenade online (thanks to Slob in the forums for the heads up). The design for their system has been seen before, but as ever non pyrotechnic simulation systems are always of interest, particuarly at sites that are pretty much tinder-box environments:
200 BBs are propelled out the nozzel of a rubber tube body by only 2oz of water (The V2s of last year had 8-10oz). Reusable, has a 15’+ blast radius from the point of impact. The kit contains a loading tool, 3 grenade bodies, and parts for 9 loads/reloads. The user will need to supply zip ties, water, BBs, and locking pliers.
They are not water balloons! They work the same as a Paintball grenade. The hit the ground bounce up and like a water rocket with out fins, they spin around and spit out bbs and water @ waist level. The Mark 3s are made from latex tube with a full 1/8″ wall (hardware store tube is around 3/32″-1/16″ wall) and will survive a full hi-cap of .25s(400fps) shot into it @ point blank range. (MilSim Labs)