Will one shot resonators. Corrosive is useful against sentients and the Orphix, as well as most units in game. Mods and Forma are listed in order of importance.

Damage and magazine capacity are the most important things here, so you can spam shots. As such, base damage mods are essential. By the same reasoning, more elemental mods are also essential. The main use of this gun is to one shot Resonators through walls and enemies from a distance. Resonators have Object Health, so you cannot get a critical hit on them. Resonators are also Status Immune. We use Gas to get additional damage from its clouds on the resonator.

Mod Analysis

1. From what I've written above, you'd think [Ballista Measure] would be useful here. That's true. But the benefit is such a small range addition you won't notice it. It also doesn't help that the mod is super rare. You actually get less quality of life because regular enemies will be harder to kill and its not worth the time to switch into your exalted weapon to kill them (especially for [Voidrig] and [Arquebex]).

2. As always, IPS mods are trash. They don't add much in terms of damage and only serve to increase the chances of an IPS status to proc over other status effects. Corrosive is more useful. These mods are essentially a waste of a slot.

3. Critical Focus and other 'aim/zoom' mods aren't worth using because they were designed with 'on-foot' Arch-Gun use in mind. They really don't provide much benefit to Arch-Guns used in your NecraMech. The ones that do just don't have space in the build.

4. [Automatic Trigger] is just a good way to waste ammo when targeting Resonators. Because they are so small, they are easy to miss. The idea with this is to one shot the Resonators anyway. Ammo economy is the name of the game for Arch-Guns because they regenerate ammo after a delay. The more quickly you shoot the less ammo you will have.