VetPlasma
 Veteran Build - Warhammer 40k: Darktide 

Chain Sword - Great well rounded option as it has amazing stagger, good damage vs any target, and really good base finesse. Obviously Duelling Sword and Combat Blade are great finesse weapons, but they make any build OP and don't need something specific built around them.

• Flak - For clearing the flak armored elites and mobs
• Unyielding  - A key target for us are monstrosities. Depending on the modifier, Elite is also really good - allows for bleed kills on ragers.

Blessings:

• Rampage - Large increase in Power - a damage multiplier
• Blood Letter - Allows for the special cancel on a slide, which will do 1800~ damage depending on the target and your perks. A single tick of damage + bleed will kill most things. Shred is a very good option if you don't like the special attack.
   

Plasma - The reason we are here, it will cleave just about anything even on uncharged shots. Carapace will still stop it, and that is it. No bosses do NOT stop your plasma shots, even uncharged. 
Headshot (charged or uncharged) will stagger mutants out of charges.
Perks: 

• Flak - This is necessary for uncharged one shot kills on gunners without crits.
• Maniac - oneshot body shots on flamers, and helps hit crit one shot on Mutants.

Blessings:

• Focused Cooling - Great synergy with Weapon Specialist as it will give you a guaranteed crit at 3 melee kills giving you a charged shot at almost no heat. Rising Heat is a great option, particularly if you don't go to the left side talent tree. 
• Gets Hot - regularly crit which will help reach quite a few one shot body shot breakpoints for elites and specials. 

You can trade out the extra Grenade perks and Always Prepared to go down the left tree and get Superiority Complex My issue with this side is that Precision Strikes does very little for Plasma gun due to its low base finesse (roughly a 7% damage increase on head shots only, depending on the armor) - It does help the melee weapon though. However Fully Loaded is a meager 33 ammo (33.75 but it always rounds down) at 80% ammo stat, which is a 12.2% ammo increase for the plasma gun since it only increases your ammo pool, not your total ammo.

You can also go down the middle tree for Confirmed Kill, but I find that the swap speed and increased toughness per melee kill helps me more for a Weapons Specialist playstyle

While Rending Strikes doesn't help the Plasma gun for anything but Carapace - it is fantastic for all our bleeding, and our melee weapon. greatly increasing our damage vs almost all priority targets.