Slug Specialist
 Veteran Build - Warhammer 40k: Darktide 

How this build works:

1. After 3 melee kills, your next shot has 100% crit chance. 
2. The Agripinaa special attack is a slug with high weakspot damage. If you give it pierce, it can tear through quite nicely. This build's weakspot damage bonuses give it enough damage to hit breakpoints it normally struggles with (gunners and flamers).
3. You shoot 1-2 times to get a kill.
4. After a ranged kill, your Rashad axe will tear through enemies very fast for 10 seconds. It will handle Crushers in ~2-4 Heavies depending on your Rashad roll (1-shot is theoretically possible) It also has a great weakspot damage stat and your weakspot buffs will make the heretics fear you (very briefly before their heads roll).
5. Repeat. 

General tips:

1. Infiltrate is a massive damage boost with this build, but also good for suppressing enemies in an AoE around you, especially useful against shooters and hordes. You generally want to leave stealth right away so that your team doesn't get all the aggro. 
2. Avoid shooting a bunch of regular shots at once except for emergencies, such as a group of Ragers when Infiltrate is on cooldown. Your main goal of shooting is to get 1 kill. Non-headshot damage isn't very good. 
3. Don't throw smokes under your team's feet unless it's a low-visibility modifier or ranged fire is coming from all sides. Even in low-vis mutators do it sparingly. Other players like being able to see. 
4. Smokes are to be thrown when ranged enemies are shooting your team at the same time as melee enemies or a boss. Toss them in between your team and the enemy, usually just barely past your team's current position. The shooters may briefly shoot blindly through the smoke but most will try to move closer to get line of sight. The goal is that when they exit the smoke they're right next to your team, allowing you or your teammates to kill them without leaving coherency.  
5. Smokes will stagger and cause Specialists to take a moment to re-find your team, so throwing a smoke at your feet can help in a clutch revive, but use that sparingly as not being able to see the enemy can be a death sentence. 
6. Agripinaa's slug Hipfire is just as accurate as the ironsight shot. It's generally good within 30 meters and is much easier to aim than the ironsight, especially while moving. 
7. Don't worry about the ranged attack speed buff from Weapons Specialist stacks above 3. It's almost never helpful. Just get 2-3 stacks and shoot something to reset your buff durations. 
8. The Rashad axe's heavies have lower damage against maniacs than light attacks, so never use heavies against maniacs. 
9. Even if you don't have a slug loaded, the regular weakspot hit kills trappers and anything weaker at a decent range.
10. Enemies that die from Flechette bleed will trigger Melee Specialist, but only if the shotgun is out. 
11. Always be on the lookout for specialists, since each specialist kill reduces your cooldown. 

"What else could I switch up?"

• Alternate Version: Kraks, Fire Team, Voice of Command. 
  • Strong build for Mostly Melee maelstrom if someone else has survivalist. Weak against shooters. 
  • You still want to reach over for Agile Engagement though. I recommend trading Bring it Down for Field Improv, and trading Demolition Team for Demolition Stockpile. 
• Alternate Version: Kraks, Survivalist, Voice of Command
  • This one is universally strong for the Mostly Melee maelstrom.
  • https://darktide.gameslantern.com/builds/9cbaca07-b10e-4102-ba1d-7082eb3cef47/slug-specialist-melee-maelstrom
• Alternate Version: Ironhelm Shotgun
  • Really really good against ragers if you hate ragers. Makes good use of Always Prepared talent, so pick that up. I drop the Surprise Attack infiltrate node for it. For blessings I recommend Run and Gun and Manstopper.
• Alternate Version: Tactical Axe 
  • Main drawbacks for the tac axe are the much lower impact and attack radius, which leaves you vulnerable to getting hit while you're hitting stuff. Special attacks can stagger Ragers easily enough. Armor also takes longer to kill since you're reliant on crits. Reciprocity helps but it's situational. 
  • https://darktide.gameslantern.com/builds/9cbace2b-910e-414c-babf-fece100987a4/slug-specialist-tac-axe
• You could take a Kantrael shotgun instead and really up your AoE damage. I wouldn't do this unless you know someone else on the team can handle long range though. 
• Scattershot IV on your shotgun is a fine substitute for Bleed. It can lead to fun shenanigans where you can get crit after crit after crit and have huge cleave. 
• Deadshot is cool, but it takes a lot of stamina and it's hard to justify putting points into the stamina talents just to make use of it. 
• The top middle talent group is also good for this build. Confirmed Kill will keep the whole team topped up on toughness when you're killing lots of elites and specials.
• If your Rashad Axe is a godroll, you could pick up 15% Elite damage talent to enable crits 1-shotting Crushers with Infiltrate buffs. It's a delight to see but not necessary for most games. 
• You can use a revolver instead of the agripinaa shotgun. It's easier to aim and you can fire multiple powerful shots in a row, but the ammo efficiency is much lower. Due to your weakspot bonuses, I actually recommend the speedloader revolver with this build but either works fine.

"Why no Keystone Modifiers?"

the only useful one here is Always Prepared, which does keep the shotgun fully loaded, but you'll be using slugs most of the time (except hordes) so you don't lose much by not having it. Generally reloading to full between fights or when you have a breather is enough. Invigorated isn't good enough to justify using Deadshot.