Shield Wall
 Arbites Build - Warhammer 40k: Darktide 

Of note

Terminus Warrant keystone seems tailored for the shotpistol. Ranged Justice grants cleave, so each shot hits multiple enemies. Helps with getting to Specialists hiding in/behind hordes, the shot goes right through. 

1 shot can hit dozens of enemies, so it's very easy to build stacks of both Ranged and Melee Justice. The extra reload speed helps out a ton as well, and makes for really satisfyingly smooth gameplay. Any other keystone would mean less points elsewhere, Terminus Warrant is pretty cheap compared to all the points you'd want in other keystones. Because they're better, but still, this build works in auric.

Made Reload Speed the dumpstat on the Shotpistol, since there's barely any difference with all the reload buffs in this build, which grants me more mobility - which the shield definitely needs.

Full Bore and Run 'n Gun on the Shotpistol has huge synergy. Run 'n Gun tightens spread, making it easy to proc Full Bore. It also opens up opportunities since you can shoot without slowing down, which is really fun.

Target Priority makes a huge difference on top of all your other buffs; The Emperor's Fist, Weight of the Lex.

Shock maul+shield does a lot of damage with all the buffs in the skilltree, so I went with Confident Strike blessing to help keep my Toughness up instead of doubling down on damage blessings. 

Opportunist means you 3-4 shot crushers, and each hit stagger them, anyway. Everything else is one- or two-shot by light attacks.

Don't forget you have a shield both in melee and ranged. You can take your time aiming while blocking in 360 degrees, you can march up towards gunners. 

Shotpistols special attack; a tap is a push, while holding the button turns it to a Heavy attack. This procs both Terminus Warrant and Weight of the Lex, buffing your subsequent ranged attacks. It also staggers a ton! You can open up Bulwarks if you hit their arm with the melee attack, then two-shot them with the shotpistol.

The talent March is probably a contentious choice, but I like the mobility it grants. One ranged hit gives you the mobility to slide huge distances. Whatever's shooting you will most likely have your shock maul or shield caving in their skull within seconds.

Can switch out  mines over grenades, if you prefer. Honestly I just think the mines look silly, impact grenades are just cooler.