Skitarii Ranged Boss - Arc Rifle - Havoc 40 READY
 Skitarii Build - Warhammer 40k: Darktide 

Ranged Arc Rifle BOSS - Advanced Combat Doctrines - Servo+Medicae Skull

The Arc Rifle boasts a highly accurate (thanks to our ability), high damage (electric), ranged AOE (from point of contact arcs to nearby enemies). And is effective (to a lesser extent) against armour.

If you like the boltgun, or the flamer, you'll love the arc rifle, as it has both of their strengths, but also the same weakness -slow reload speed- so we fix that by taking the talent Gunsmith; so that our magazine refills automatically while we're using melee.

The Arc Rifle already has high Flak damage (see weapon attack breakdowns) so I chose to refine into +25% Maniac/Unyielding damage, to bring the high damage up to par against key enemies (Ragers, Mutants, Trappers, Flamers, Bombers / Ogryns, Reapers, Bosses).

Our ability Advanced Combat Doctrines, boosts our accuracy, rate of fire, crit, cleave and damage, significantly. And with our ability nodes, curios, and Redline Capacitors Keystone, we have a -very- high uptime with our ability.
You -can- use this weapon to horde clear effectively -but- you're going to chew through ammo fast on Havoc 40, so use more cautiously especially if there are other heavy ammo users in your group.

Aura: We've chosen Ammunition Deposit, because currently most groups are comprised of Skitarii, so we're making sure we take an aura the others likely won't have. But! Foe-Render Creed is the better choice for us.

We can take this aura by swapping out our Servo Skull & Medicae Skull blitz, for Adaptive Combat Calibration and Uncapped Arrestor - which will improve our melee capabilities as well.

Curios: chosen to mitigate Havoc's -45 Toughness and a -35% penalty to base Health. Only taking one 20% Damage Resistance (gunners) due to diminishing returns.

The build offers a high DPS rate (at a safe distance) vs bosses, similar to that of a Hivescum. The added advantage is, you melt down the boss, while the rifle arcs to nearby enemies; therefore horde clearing as well during those crucial moments. 

For Melee we take the Arc Maul because we're already spec'd into electricity nodes for extra damage for our Arc Rifle.
The maul provides us with decent damage, it's special attack boosting damage and arcing out for better horde clear.
Primarily we take the maul for it's safety. It has high stagger, and if you mix blocks (as you should) into your attack pattern, Lightening Reflexes becomes beneficial, but if that isn't to your liking I recommend Enhanced Voltaic Arcs for better AoE Melee.

Good luck, and remember "Optimal performance is rewarded with modification."