Maybe it’s like the one in the current Dirk Gently.
It fires air but no moving parts.
I want one of those! Non lethal but kicks ass in close quarter combat. Of course it goes against all laws of physics. It sends the person flying but barely has a kick felt by the shooter. In real life that can't happen. Anything strong enough to send a person flying like that has to have a kick strong enough to do it to the shooter too which is why something that powerful is always mounted to something like a tank, bed of a truck, on a fighter jet, or helicopter. Think .50 cal mini-guns. :D