AoE Toughness dispenser Bullet Hose Veteran
 Veteran Build - Warhammer 40k: Darktide 

Purpose of build: Melt almost everything with Vraks Mk V Infantry Autogun , while replenishing AoE Toughness to squad.

Two parts of build:

1. Melt everything with Vraks Mk V Infantry Autogun:
Gun is insanely good at finesse damage. Marksman's Focus is great here for adding more. Executioner's Stance helps with recoil, damage and extra weakspot damage. Precision Strikes adds even more.
 

2. Replenish AoE Toughness to squad:
Born Leader is the key to do this, the 50% coherency bonus is amazing for multiple other passives such as Close Order Drill, Field Improvisation, Survivalist and the replenishment itself. While the 20% toughness-you-gain shared to allies doesn't sound like much, it adds up from multiple sources rather quickly. We boost this by taking most toughness-replenishing talents we can (Executioner's Stance is one of them!!) without sacrificing the core damage of the Vrak V, and further buffing these replenishments with Tunnel Vision + Long Range Assassin.

Toughness replenishment sources and how much is shared with allies:
You get 60% toughness replenishment (TR) bonus at 15 stacks of Marksman's Focus from Tunnel Vision, and then calculate the 20% we share to allies. For easier math we will round this down to 50% TR (to also account for not being at 15 stacks all the time).
Instant sources:
Default game replenishment on kill 5% + Out for Blood > 10% instantly on kill > 15% buffed > 3% to allies
Confirmed Kill  > 10% instantly on Elite/Special kill > 15% buffed > 3% to allies
Covering Fire  > 15% instantly on any ranged kill if they're close to the target> 22.5% buffed > ~4.5% rounded to allies
^ note: this gun is not really a sniper build obviously. While you can poke at long range in a pinch, it shines best in close to mid range (see blessings), so this talent is a synergy for that + our toughness regen build flavor, instead of Longshot.
Exhilarating Takedown > 15% instantly on weakspot kill > 22.5% buffed > ~4.5% rounded to allies
So, you give to your allies instantly:
- 15% toughness for an elite or special ranged weakspot kill:
- 12% for any enemy weakspot ranged kill;
- 7.5% for any enemy ranged kill;
- 10.5% for elite or special weakspot melee kill.
- 7.5% for any enemy weakspot melee kill. 
^ You get any of these values per kill. That's a lot if you think about a horde and how fast this gun melts things.

Over time sources:
Confirmed Kill  > 20% over 10s on Elite/Special kill = 2%/s > 3%/s buffed = 0.6% per second to allies
Executioner's Stance  > 10%/s > 15%/s buffed > 3%/s per second to allies

If we take into account that we removed 10% TR for easier math, per second regen is close to 4% at max EO stacks, for all allies.
If you want to exaggerate a bit, you can even multiply all these regens by 3 on paper since you have 3 allies :D

Apart from this, any toughness that you replenish from allies (I think) also gets shared from you at 20%, such as Zealot relic, Psyker Bubble, and a bunch of other passives.

All these added up make for a very strong toughness dispenser without sacrificing damage at all.

For melee you can flex w/ev but I prefer Power Sword for its cleave, carapace damage and overall effectiveness. The lack of Trench Fighter Drill is not really felt since its a pretty fast weapon by itself.
Next step is to test if Withering Fire can be a good enough talent to replace Field Improvisation in less-than-Havoc gameplay.
For Havoc 40 I would remove Long Range Assassin (losing 20% Toughness Replenishment aka max possible 40% instead of 60%) for Grenade Tinkerer to guarantee crusher kills and more monstrosity damage, against whom you can't really regen a ton of toughness (no high kills number) so the quicker they die the better. If no kraks, focus to pick off elite/specials around to tougheal team and clear the bossfight area.