So as some may or may not know, the Lightning Gun does not have a consistent duration nor a consistent damage per clip. It is also not exactly know what the Damage Value in the gamefiles exactly does.
I did some testing myself and I have come up with the following conclusion:
The Lightning Gun Beam has 6 rays, each dealing 5 damage per tick (0.2 seconds). The rays do NOT nessesarily connect at all times, meaning that they dont do damage. Each ray can and will do a maximum of 150 damage. Until ALL 6 have their respective 150 depleted, the gun keeps firing and all rays will try to continue to do damage. The displayed capacity scales with the highest damage value of a ray remaining. This means that 1 point of capacity is only drained (during 0.05 seconds) when the capacity percentage is above the percentage of the damage remaining.
I addition to that, at the beginning of the beam, each ray has a chance of dealing 1 to 2 extra damage.
The minimum duration of the Lightning Gun is therefore 6.0 seconds (150/5 * 0.2) and the maximum amount of damage possible is 912 (1506 + 62).
Let me give you an example of what I mean here:
0.00s: 8 Initial damage is done, all 6 rays connect for a total of 38 damage
0.20s - 5.80s: All 6 rays hit every single time, dealing 30 damage per 0.2 seconds
6.00s: Just 5 rays connect, 1 misses. 1 of the 5 rays has dealt 2 + 305 = 152 damage, 4 rays dealt 1 + 305 = 151 damage. The one that missed only dealt 2 + 29*5 = 147 damage.
So the capacity will be drained until 2 points are remaining.
6.20s: Since there is still capacity left, all 6 rays will fire for 5 damage.
6.25s: Last capacity point starts draining
6.30s: No capacity remains. The visual effect of the lightning fades.
Overall the Lighting Gun dealt 8 + 3065 + 5*5 = 933 damage in 6.30 seconds = 148 .095 dps.
Now of course, this is ideally speaking. You will miss a lot more rays in the usual game. If you want to see a 6 second duration with 906-912 damage, play Nest and attack an shell-less Egg from very close range while aiming downsights.
Here a picture of the 6 rays, where only 3 connect