the Berserker
 Veteran Build - Warhammer 40k: Darktide 

One of the first builds I ever fell in love with and refined. Tactical axe has always been one of my favorite melee weapons and with the addition of the +30% Weakspot damage perk on Veteran it got really good.

General "optimal" flow goes something like this 

Use the Bolt pistol to kill an enemy-> swap to melee to activate Melee specialist and go to town (You should aim for the head of course) -> ideally build up to 10 stacks of ranged specialist-> swap to bolt pistol, rinse and repeat. Use the Voice of Command combined with Duty and Honor when you feel like you're getting overwhelmed or when your toughness is running low to keep yourself in the fight longer. It should be noted that you don't have to build up full range specialist for this build to work so feel free to swap to the bolt pistol at any time to take out those pesky Bombers and Snipers

 I've found that Tactical Axe really shines when you give it Attack Speed and Weakspot/Crit buffs, while it doesn't have the same one shot potential as the other Assassin weapons it works great at chewing through enemies, especially when you don't have the time or space to charge up a Heavy attack

 You can also switch the bolt pistol to the Explosive Mark and swap the Point Blank blessing for Lethal Proximity to give yourself a Human equivalent to Ogryn's Grenade gauntlet, it gives up being able to easily tear through tougher enemies in one shot in exchange for some great crowd clearing.

I personally like building all rounder builds so this build gives some great flexibility for dealing with just about any kind of enemy.

 I don't play anything above Damnation so I can't vouch for it for anything beyond that