Zapinator 9000
 Skitarii Build - Warhammer 40k: Darktide 

Overall Concept

This build ignores almost all survivability for the sake of a fairly consistent +150% damage and +30%. This turns the Branx Mk IV Arc Rifle into one of if not the most powerful ranged weapons in the game, combined with incredibly good ammo efficiency and fairly decent ammo generation this build WILL top damage auric maelstrom or at least be a strong contender without picking up much if any ammo. This is even a viable build for no ammo pickup missions so long as you are more conservative with your shooting and only use it to clear large elite hoards. I have not tested it in Havoc 

Playstyle

This will primarily play like a weapons specialist veteran. Using the heavy attack pattern of the Branx Mk XI Paired Transonic Blades to get as many headshot kills as possible off light hoards for Reactor Coil Recharge (I recommend setting your height to minimum to make headshots more consistent). This is enough to sustain Advanced Combat Doctrines as you only need it for brief bursts most of the time, however if you find yourself requiring more capacitance dropping Weakness Analysis Doctrine or Servo-Core Recharge Engine for Flux Conduit Build-Up should be enough of a boost. 

Whenever you see a large group of elites or heavies activate Advanced Combat Doctrines and simply hold M1 until there is no longer a large group of elites or heavies. (Shooting Bulwarks in the exposed arm is also viable and should allow the arcs to bounce off of them and hit other Bulwarks in the back/sides). Dumping a entire magazine into a large hoard containing elites is the optimal damage output and the ammo efficiency is enough to sustain it comfortably, you should be mindful about how much you are shooting but not worry about it, I can shoot almost a entire game only picking up a handful of small ammo pickups or a single large ammo bag. I at times will dump two magazines or even more into particularly large hoards, the longer you shoot the better the Branx Mk IV Arc Rifle becomes as more enemies become electrified Calculated Priority stacks and Writ of Ammunition Enumeration reaches +30% fire rate that is a massive boost to Branx Mk IV Arc Rifle damage due to it spreading electrified faster. (Advanced Combat Doctrines does not drain capacitance while reloading). Weakness Analysis Doctrine in my experience is enough to sustain Advanced Combat Doctrines for quite some time and even go slightly positive on capacitance. 
 

One of the more important things when it comes to ammo conservation, especially since you are not spamming your ability like with Chordclaw Strike. Is to use and abuse Noospheric Command at almost all times. It is a incredibly useful tool to remove specialists, disablers and elites, it will even stagger gunners out of their shooting animation. It can easily be triggered while in melee (I recommend making a macro to double tag or simply using single tag companion just be mindful about tagging pox bursters), and in my experience will consistently kill 2-3 elites especially with Infernus stacks. This is Skitarii's version of Blades of Faith and it should be used in the exact same way, this will save you a large amount of ammo over the course of a game simply picking off stray enemies rather then using your Branx Mk IV Arc Rifle.

This is fundamentally a backline support build, you should be in melee but as soon as melee becomes dangerous you fall back and start shooting. You really shouldn't even be engaging more then one or two raggers without switching to your gun, and you should not be pushing into areas first. You are rather delicate but playing more as a DPS support like a Psyker will net you good results with the added bonus of being able to revive anyone who does go down easily with Medicae Servo-Skull. Do melee but prioritize shooting when the situation demands it.

Why no Purgator Servo-Skull 

While a good and rather high damage potential blitz, its not an amazing blitz and tends to fill the same role that activating Advanced Combat Doctrines does (shooting into large and tough hoards). I find that you kill enemies fast enough that it is unlikely you will actually get much benefit from Purgator Servo-Skull and simply saving the grenades for Medicae Servo-Skull is a much better use generally. Not taking Purgator Servo-Skull also ensures that you do not accidentally waste a grenade on it while trying to revive someone. Overall while Purgator Servo-Skull is good, I find myself rarely if ever using it and that last trait point is better spent on other things.

TLDR

Weapon's Specialist Veteran but with even more damage, useful servo skull revive, and a servo skull with a infantry lasgun that has infinite ammo.