This is not in depth suggestion, but I do some complicated calculations here.
Okay, first I want to cap hypergun’s base firing rate to 5/sec.
Then make its damage per salvo linearly growing. 150 on 0 fp, 300 on 1 fp, and it would be 1800 on max fp.
And this is the main point of the suggestion, “The longer you hold fire button, the faster it shoots”. So if you hold the fire button, it starts to accelerate the firing speed.
On 0 fp its max firing speed is 2x (10/s) and it increases so on max power is 4x (20/s).
The higher its level, the faster it accelerates, on 0 fp is 4 sec to reach top speed, while max power only requires 2.5 sec.
Overheat rate is based per volley. If it shoots faster, then it also overheats faster. So you may want to use it in burst on higher fp. Maintaining overheat rate will be harder at higher level, but it gives an advantage for fast response high dps.
That’s what I would call Hypergun.