Plasma instaplode

I have been trying to figure out if the plasma nades in this have conistant instasplode if one sets off another. So far, it seems to be random. Sometimes it instasplodes, sometimes it sends the nade off and it wants until it lands and then explodes a few seconds later.

Walshy had posted a video about plasma nades and how to utlize the instasplode, but it appears as though he is incorrect about how these work in Halo 4. Can anyone confirm? Perhaps I am doing something incorrect.