Just another Plasma Vet (Havoc 40)
 Veteran Build - Warhammer 40k: Darktide 

Bound by honour update:

Melee options: Maccabian Mk IV Duelling Sword Catachan Mk VII "Devil's Claw" Sword Catachan Mk VI Combat Blade Rashad Mk III Combat Axe 
Aridin Mk I Power Falchion Munitorum Mk I Sapper Shovel Anything you're good with and can survive with

Viable in havoc 40 

Plasma took a bit hit by not going through carapace enemies anymore but kraks solves this

Shredder Frag Grenade is much better than krak on Maelstrom/Auric missions and below. They can be used in havoc 40 as well but you need to combo them with a meele weapons with the Uncanny Strike blessing such as the knife/shovel/duelling sword

You can ditch Always Prepared and M35 Magnacore Mk II Plasma Gun for another weapon entirely and take anything else you'd like. Good options are either Onslaught for the Accatran Mk XII Recon Lasgun or Serrated Blade to be more of a melee powerhouse using any weapon but specially with the Catachan Mk VII "Devil's Claw" Sword, Munitorum Mk I Sapper Shovel and Catachan Mk VI Combat Blade with Uncanny Strike and Mercy Killer. It depends on your weapon/playstyle focus.

In tandem with discarding Always Prepared, you can also take off Grenadier to have 2 points for Toughness Boost and Bring it Down! or Stamina Regeneration Boost and Shock Trooper if you're using the Accatran Mk XII Recon Lasgun (also swapping Exploit Weakness for Onslaught )

-----

Old stuff from 1 year ago before havoc was even out below.

Usage:
Just need practice with delayed shot and activating the power sword to counter everything in the game. You can how to approach each engagement, the only necessity is to rotate weapons mid engagement which should happen naturally.  If you're engaged in a meele you can quickly swap and snap shots at things and if you have distance you can spam your plasma shots to kill something, anything, to do the same to start a very narutal cycle to trigger Weapon Specialist + Agile Engagement. Spam granades on monstrosities/lesser monstrosities, you can time your grenades with voice of command to stunlock it and possibly solo it.

Configuration/Items:
Can swap the plasma for revolver(Hand Cannon + choice blessing) and plasma sword for the rashad combat axe(Headtaker + Brutal Momentum blessings) for virtually the same effect but less wave clear. The power sword needs power cycler 2, it can do without momentum but if no power cycler then go for axe. Build is strong af so you can have fun using any other weapon configuration too. Example: The nodes above weapon specialist can be swapped from left to right side to take onslaught if you want an autogun/lasgun/etc.

I found these curio blessings to be optimal but the perks can be changed to your preference. 
 

Alternative:
You can sacrifice Close Order Drill, Confirmed Kill and Grenade Tinkerer if you swap the krak for the smoke grenade so you can get more 5% ranged damage, Precision Strokes, more ammo with Fully Loaded and Superiority complex ((You don't need this damage and it might pay off to be tankier and have kraks but this gives you a lot of damage to compensate Precisions Strikes(your power sword/combat axe benefits with Brutal Momentum blessing, the plasma gun on weakspot hits too, of course) and Superiority Complex and you're plenty tanky with just Voice of Command, Duty and Honour and Iron Will stacked so use what gives you most comfort)). In this case you can swap longshot and volley adept for close order drill and confirmed kill to be extra tanky, or for vanguard and out for blood/tactical reload for extra mobility. 

Build/number wise this grants everything you need to clear up to auric maelstrom/karnak hard mode with confidence.