Embraced Castigator | Damage Resistor
 Arbites Build - Warhammer 40k: Darktide 

Currently feels very comfortable in Havoc 20-29, will update once I've reached higher ranks.
You basically have near constant 50% damage reduction during hordes.

The Bad
- Heavy ammo consumption
- Not the best setup for Monstrosity damage

Playstyle
2nd or backline Gunner.

While the build dips into a lot of damage resistance, the front player should probably still be a Zealot or Ogryn. I consider the main weapon the Gun and not melee, so you should remain behind who ever is engaging. Gun down anything ranged as you advance behind them. Don't over do it, as you'll be hogging ammo from everyone if you're constantly shooting. Prioritize elites Gunner/Shotgunner.

We have no cooldown reduction, so use Castigator Stance when needed rather than when it's available. This is usually when fighting Captains/Monsters or to allow your team to pass through a gunner heavy door/corridor. Also a decent panic button when surrounded. The Braced Auto has a lot of stagger and suppression, you simply need to shoot in their general direction and they go for cover. While in Stance, you can sweep over a room or gunner balcony to provide suppressing fire for you team to enter unharmed.

Because the gun staggers so much, a few shots in a group of heretics brings your Forceful stacks up to max.

When fighting monsters, Tag your dog to it, and try to interrupt its grabs/charge/melee combos as best you can with your Remote Detonation. There is probably someone else in the team who can do more damage to it than you, so just try to keep that person healthy.

Loadout

I go with 3 Health curios, your mileage may vary but from what I've tried it seems to pair better than Toughness curios when playing with True Grit. In Auric at least, the setup has enough passive toughness regen and damage resistance that you can go through hordes without a scratch, and then high health gives you prevention from high damage hits like crushers and snipers.

The Braced Auto with Inspiring Barrage is the focus, but you could swap speedload for anything else you prefer

The Arbites Maul is just all round good, you can pick which ever melee you prefer. I have relentless strikes on it to help with large targets as it kills anything else without too much effort.  - Light, special, heavy - bonks ragers

Notes
Adamant Will is a better pick than Ammo Belt if you can manage your ammo properly.   (forceful keystone mod)
No Escape might be a better pick than Withering Fire.    (the first passives)
Rebreather is probably not necessary on lower difficulties.  (bottom middle row)