Veteran Shredder
 Veteran Build - Warhammer 40k: Darktide 

Based on a build found here: https://steamcommunity.com/sharedfiles/filedetails/?id=3062261689

Relies on the combination of 10% passive shredding, the power of the marking keystone, and the brittleness passive in the right tree to allow the columnus autogun to rapidly kill literally any target in the game. Doesn't kill crushers quite as fast as a dedicated plasma gun build does, but in exchange the gun shreds everything else too (including bosses, faster), while not having to worry about heat.

Shredder Flavor pick is are Longshot, which can be swapped for Target Down!, and taking the left tree vs middle shouty with grenade regen and Duty and Honor, which frees up another skillpoint to be spent wherever you see fit (volley adept is nice, among other things). 

The rest are pretty mandatory. Stay away from Exhilirating Takedown until they fix the bug that makes it hurt you instead of protecting you. 

Alternative ranged weapons: Any other fast firing autogun/lasgun - I just think the Columnus mk5 is crazy right now, and definitely far above the others. 

Alternative melee weapons: any power sword with power cycler 3 or 4, or a chainsword. The other catachan blades work too. Really all you need is something that can protect you from hordes and conserve ammo when necessary. Catachan mk1 has the added bonus of parry, which can 1 shot ragers with the right perks and can protect you from crushers without spending stamina if they get too close, as while your TTK on crushers is very good, your guns don't really stagger them (ideally you have some distance, or dodge them well, but in a pinch having a weapon that can do this is nice).