Northerner
I am here with a new design, and I have discovered a large bug which might be causing issues with railguns combined with other weapons.
First the ship:

Price: 2374400
This is the Doomsmith, using superior tactics (being the enemy getting rammed by medium ships, then getting swarmed by smaller ships.) he is able to vanquish the mighty Mjolnir... If the AI is set correctly...
Look at the difference:
Normal AI:

Now the arena AI:

And this is not a random luck factor, the Doomsmith always wins on normal, while Mjolnir always wins on arena. On arena AI for some reason the rail-Doomsmith decides to aim it's small lasers (I put them there against small ships trying to flank) at the enemy instead of it's railguns.
I think you might want to look into this.
(Edit: Arena AI sometimes works as intended, but not always.)