Marksman
 Veteran Build - Warhammer 40k: Darktide 

Basically ADS and click heads. Try to take 1-2 seconds between shots, 2 full seconds is about +60% crit chance. If you're patient, you'll be critting almost every shot, and 1-shotting everything except Ogryns, which will usually be 2-shots. Maulers you should shoot in the body, and don't bother shooting Crushers. With the massive Finesse and weakspot bonuses on this build, and the +100% critical weakspot bonus from Deadly Accurate blessing, the damage is insane.

The real kicker is the keystone ability modifier Tunnel Vision. That toughness replenishment bonus goes to +50%, but with  Long Range Assassin modifier, your stacks go up to 15, and the toughness replenishment bonus goes up along with it to +75%. This bonus multiplies the toughness gained from Exhilarating Takedown and Confirmed Kill at the top of the tree, including the toughness-over-time from CK. All told, this talent combination alone will equate to about +44% toughness regenerated on headshot vs a non-elite, +79% vs an elite. It even combines with Catch a Breath, giving you about +9% toughness per second. Combine that with Iron Will and you basically become a ranged tank vs ranged enemies. As long as you can keep up Executioner's Stance and keep clicking heads, especially on elites/specialists, or even just shooters, you'll barely take any damage.

The mk VI Power Sword is crucial for its Push Attack combo, where a Push Attack comboes directly into Light 4 (an overhead Strikedown with high damage and armor pen) allows you to 1- or 2-shot most elites, including Crushers if you have your Slaughterer stacks up. Plus the bonus crit from dodging thanks to Reciprocity makes it ez pz.

You could take third Toughness curio instead of Stamina for even more toughness gains from headshots, but you'll be doing the push attack > light combo a lot, so the extra stam helps.