Leh Charge Knife new ver
 Zealot Build - Warhammer 40k: Darktide 

Combo for generally everything Heavy + push attack and repeat/loop you shouldn't run out of stamina and be on a net 0 gain make sure to always dodge when doing the combo and at the 5th dodge, dodge backwards and slide so you can reset your dodge timer (if your confident in just resetting it normally do that)
 

if you want something dead fast, i.e crusher/mauler/bosses spam push attack on their head, hence why I now run desperation compare to the old build. once you run out of stamina you can do heavy, special attack (vent on plasma gun) heavy and resume to heavy attack spam: Or if you cannot be bother to do that combo just go for heavy + push attack repeat, you should be able to do this even at 0 stamina since you just regen enough stamina to do a push attack. 

Reason for las pistol is because you can do 1 knife into 1-3 shots with laspistol, one if you crit with it since sometimes i cannot hit head with knife

edit: now using db since thats the way we deal with horde clear since the game has remove the aoe crit cd. Now that we cannot spam as often since the game remove aoe crit, we cant get 100% uptime on Fury of the Faithful attack speed for instant heavy push attack combo, so now we also drop enduring faith for faithful frenzy. For the knife you can go precog or riposte. I find that precog does more burst dmg but riposte is just more consistent so i use that one