Heavy sword
 Hive Scum Build - Warhammer 40k: Darktide 

This looks troll but it works, Perfect Strike lets you cleave carapace and it reduces enemy hit mass by 75% on crit. This combined with the massive power boosts (which amp dmg, impact, and cleave) gives you absurd levels of cleave on crits. You can sit around 65% crit and 80% when the stim is running. 

Cleaving carapace means you can actually stack Bladed Momentum when fighting elite packs, and you have enough attack speed to keep those stacks up fairly reliably. The single target combo is H -> Special repeat. For hordes with no elites just spam lights to fish for crits and stack up Hyper-Violence . With elites use the single target combo and it still hits plenty of enemies.

Needle pistol is your answer to crushers and specialists/gunners. With run n gun and stripped down you can sprint at gunners while shooting. This also procs Regained Posture so you can keep sprinting forever when enemies shoot at you. Boom bringer is for when a TON of elites spawn. I wouldn’t use it on bosses outside of emergencies since you can just shoot them with the pistol to stack chem dot and then single target combo them with the heavy sword.

The heavy sword scales really hard with attack speed since the weapon special is improved by it and its a relatively lengthy animation. I run two +3 stam curios (make sure they are at least 410 rating or they only give 2 stam in game) to maximize this, combined with rampage you can attack at martyrdom zealot speeds. Having another scum running stim supply with attack speed and/or crit chance feels great with this build, since an allied stim crate will now stack Chemical Dependency . You can be a lot more selective about when you use your stim since their stim supply will keep your keystone stacked.