ratatatatatatatata (Maelstrom/Havoc)
 Hive Scum Build - Warhammer 40k: Darktide 

A build that is suitable for higher difficulties and will let you never stop firing. 
We are using  Branx MkIII Dual Autopistols  to kill pretty much everything except Crushers. 
Branx MkIII Dual Autopistols will SHRED almost everything with your Enhanced Desperado up or stim. The exception is Crushers/Carapace Armor. You need to use melee when going against Crushers or use blitz if overwhelmed.

Maulers and Plasma Gunners can just be shot in the legs/knees where they have flak armor instead of carapace.   

Use stim asap and keep dependecy up. Stim can be used as extra damage as needed.  

You can also use stim to go into melee to fight crusher hordes or other meaty hordes where gunning isnt as much of an option (or just shoot them with a rocket)

Use Branx MkIII Dual Autopistols against every enemy except crushers (When ability or Stimm is up)

Melee is useful against Crushers and sometimes Bosses (If out of ammo and out of ability and can't mag dump anymore, Improvised Mk I Shivs do a solid amount of boss damage), making a bit of space or needing extra mobility or blocking.
 

Boom Bringer is best emergency blitz in the game. Shoot at feet to clear space, Shoot at crusher horde, Shoot at boss if you can refill grenades quickly after or if overwhelmed by multiple bosses. Shoot to rescue teammates from Beast of Nurgle or Chaos Spawn

Vulture's Mark vs Chemical Dependency 

For a ranged build, Vulture's Mark looks better on paper. 

Ranged damage, Movement Speed, and Ranged Crit Chance up to 15% (5% per stack, up to 3 stacks) With a 8s (12s with the additional talent) 

The problem with Vulture's Mark is, all stacks fall off after the timer. This means in between packs of elites/specials you may have it fall off. Or if teammates are getting the killing blows.

Theoretically Vulture's Mark is pretty good and you can get some good value. Vulture's Mark might be considered and will definitely be considered if it gets buffed in the future

Chemical Dependency just has guaranteed uptime for an entire mission, and has powerful effects also. 

At max stacks, 30% Ability Cooldown Reduction (Meaning more uptime on your +15% rending and your stacking ranged damage buff up to 15%) 
Plus 15% Crit chance for both melee and ranged, and 15% Toughness damage reduction. 

On top of that, it also makes your melee better (more crits = good)

This is extremely worth in my opinion and is why we have it in this build.