Heed is making this???
I have a model and stuff, but the only good way I can think of doing this is making it hand help with two hands, like a handheld cannon

but more modern, then have it change the playertype so you cannot move while shooting it.
Or I could make it so you right click to spawn a vehicle (ai player like all other turrets) and get mounted to it, and when you dismount, it goes away.