Perfect Block Arbitrator
 Arbites Build - Warhammer 40k: Darktide 

Perfect block stuff for big buffs. Using ability grants you 25% dmg for 6 seconds and Arbites Vigilant gives 25% strength for 12. Both of these affect your nade so try to throw one right after charging(and clumping enemies up). Use your melee weapon special flashbang to instantly get back to 10 stacks of forceful. That special recharges over time and from blocking melee/ranged hits with the shield so you should be using it often. It provides a lot of breathing room.

 Also try to underhand the grenade (theres an alt fire keybind for underhanding nades), and arc them over the front line of the enemies. If you land it right you can kill tons of enemies. If you need immediate stagger then just overhand throw them at the front line. The bolt pistol Lethal Proximity affects your nades, all the time. You dont need the bolt pistol out when the nade goes off or anything, just get +25% range always. You could take the shotpistol with this build too for more block synergy, you probably want no respite and pinpointing target/full bore on that weapon. 

You have pretty bad boss damage but can deal with captains/twins very well. You can block enemies for a long time so you should try to hold as much aggro as you can to take pressure off your team.