Try this: SKRJK
Use secondary attack (Self-repair button) while in ultimate to shoot rapidly.
Rule uses the primary attack button spam with button allow and disallow to make it work, so I was currently unable to make it shoot on primary attack button press.
Put wait timers and other logic to make it shoot the way you want it to.
If you can find how it could shoot rapidly and stop when the primary button is held and not held, please reply to me.
I would also like to add it on primary attack to my ult on bastion.