Godmode Gunslinger
 Hive Scum Build - Warhammer 40k: Darktide 

This build guarantees infinite ammo and infinite range immunity almost 80% of the time. You pop the ult and after it finishes you pop the stim which allows you to generate the ultimate back in seconds. Rinse and repeat, you've got yourself a class that basically is immune to range damage, has infinite ammo and almost never relies on melee. (I say almost because you still have to use your melee for crushers). 

I chose Blackout grenades because it provides the most utility. You are free to choose the gas canisters (which are arguably broken for what they do) But I prefer the utility to stagger enemies and the constant replenishment over time. The grenades are useful for staggering enemies on the ground so you can finish them off execution style (especially for Bulwarks). Also the Pocket Toxin node makes the Blackout grenades a good hoard clearer and provides good damage against elites ontop of the stagger.

Aura is the Gunslinger Improved. This is self-explanatory, its there to maintain your ammo and as Hive Scum you should rarely be picking up ammo (leave them for your vet rejects, they need it most), thanks to the pickpocket perk which allows you to get 20% of your ammo back up to 20%. 

Lastly is chemical Dependency, which i can confidently say is the best keystone for Hive Scum. Since You'll be popping the stim very frequently, it guarantees not only a total of 30% cool down reduction but 15% toughness damage reduction and 15% crit chance (I don't have to explain why this is HUGE for Hive Scum and especially with this build). You can even go for the Maxed Out Chems for an extra +1 stack, but you'll have to sacrifice one of the other nodes for that. If you really want to you can relocate the 25% weak spot damage to the Maxed Out Chem node.

For Curios I go for toughness, toughness and Health. With 4% combat ability cooldown on all 3. The other perks are up to you, I prefer extra toughness and faster revive speed for those clutch moments.