I recorded this today as a Elder Sentinel Scattershot. Spits are pretty RNG. Even when I was spitting from 1 tile away (PB range) there were missed spits. Some spits didn't even land from 3 tiles away. Also the cooldown was anywhere from 3-5 seconds. (lag was effecting stuff)
Gonna try and test it out some more and what solo fights look like. If I'm lucky enough to get a PB it knocks down a marine. I think you need 2 PBs to put them to sleep for a while. Buckshot still stuns though, even when you don't land a PB.