Thanks for the feedback, so the b4 anti tank ability is bugged, the tank must sit still for the ability to work? That leaves the part about the muni credit unexplained though.
As far as I know (I haven't used it for myself yet) the B4 can shoot at moving tanks while they're in the B4's radius.
But the rotating and aiming time is very very long so it will take a while until it actually shoots.
The video however seems to show a bug.
As DarthBong stated before the B4 is bugged as hell.
Sometimes it rips apart all the tanks, sometimes it doesn't do a single shot.