Hamdol's Melee Hive Scum - Havoc 40
 Hive Scum Build - Warhammer 40k: Darktide 

STIMM IS A HYPEX(CDR on Melee) STIMM WITHOUT ANY OTHER INVESTMENT.
SHOULD BE A %50 VISCOSITY 45s CD STIMM!

Hi, my name is Hamdolsun, I'm a long time veteran and playtester for Darktide.
Idea with this build is: 

When you have rampage and a decent sized enemy pool / important target, you pop rampage and stab everyone until they die or you run out of rampage.
The moment you run out of rampage, pop your stim. You can use the ranged attack immunity on your pistol to run away to a safe spot if you want to. Kill things until you get ability back. Rinse and repeat.
Remember that you have infinite ammo, so you can just use your needle pistol to kill a lot of enemies in your downtime.

Hyper Critical will let you mulch mixed hordes with light spam.

For curios: One stam for extra attack speed and mobility, two toughness for not dying.
You can drop +HP for +Ability Cooldown on curios but I like not dying to a single burster a bit more. It can help you cycle to rampage faster. 

The only ranged investment here is your grenades and infinite ammo from pickpocket.

Mk II Needle Pistol for single target dmg on demand for big targets/specials and horde clear in alt fire.

4 Chem grenades for area/armor clear on demand.
You can play flashbangs with this but you need to drop Hyper Critical and go with +3 stacks of toxin on grenade explosion.
The reason for this is Hyper Critical not giving you stacks on insta-kill.

Enjoy killing everything. Keep up the cycle and you'll be fine.