Chainaxe Deputy; Chainsword Rise Up Build
 Arbites Build - Warhammer 40k: Darktide 

Disclaimer:
Chainsword as of 'Bound by Duty' update has been buffed... however it did not made it much better than it was before and its still considered a mediocre weapon... However in the hands of an Arby it can shine... even if the shine is a little dull...
TIPS:
1. Range weapon is a personal choice but You should have a quick response one in order to deal with incoming Specials and the fact You will be at the frontlines where Flamers and Trappers will be coming after You
Breakdown of best choices from Top to Bottom Tier:
A) Revolvers (preferably Zarona; its nice at sniping if You don't get suppressed and can use Gloryhunter for good toughness restoration when fighting Elites while Agripinaa is great againts Unyielding but falls off at long range engagements due to accuracy spread)
B) Bolt Pistols (Lethal Proximity makes Arbites Grenade radius absurd and Puncture does not need explaining how good it is; You could also consider Gloryhunter for good toughness boost when fighting Elites)
C) Exterminator Shotguns (preferably Mk VIII because of tight spread and useful brittle slug for Your Chainsword, both fall off at long range engagements)
D) Combat Shotguns (preferably Agripinaa for slug shots which is usable at long range engagements or Accatran for burn DoT utility and suppression)
E) Shotpistol (offers nice protection againts range attacks when caught in the open or peeking over covers while under fire; falls off at long range engagements)
F) Shredder Autopistol (falls off at long range engagements but its great at staggering; can accumulate Forceful stacks fast)
G) Infantry Autoguns (they do not pull as fast but compensate with the rate of fire and acceptable long range capabilities; can accumulate Forceful stacks fast)
H) Braced Autoguns (they do not pull as fast but compensate with the rate of fire and suppression; they fall off at long range engagements; can accumulate Forceful stacks fast)
I) Vigilant Autoguns (they do not pull as fast but they have acceptable long range capabilities; long reload speed and poor reactiveness makes it not as preferable in comparrison to other options)
J) Double Barrel Shotgun (falls off at long range engagements; less preferable)
K) Boltguns (Very slow to pull out with a very slow reload; best not to take it for this build - Your Chainsword should do enough againts big targets and Your ability Break The Line with grenades give you enough CC to deal with masses)
2. You can use Shock Mines instead of Arbites Grenades however IMO Arbites Grenades are better due to damage, reactiveness and Boss stagger capabilities
3. Despite Chainsword not being recognized as a stagger weapon taking Consussive talent is still mandarory due to how it interacts with Force of Will talent which allows You to regain toughness even when You will be fighting Bosses
4. Combining Impact Boost and The Emperor's Fist talents allow You to stagger a Crusher with a Heavy Attack Rev on the head; 1 Forceful stack allows you to stagger it with a Heavy Attack Rev on the body!
5. I tested both Mk IV and Mk XIIIg marks for Chainsword with this build and here is the rundown of it;
Mk IV has good moveset all things considered and together with revs being faster to finish it gives more value overall when You fight multiple enemies (due to it being faster = safer to execute especially when surrounded). Push Attack has its moments but overall its not great
Mk XIIIg has always been considered better which IMO is a mistake; moveset is clunky (Your horde clear needs to ALWAYS be initiated with a Push Attack which is good but considering overall combo its not great. You can spam Light Attack if You get high attack speed however but so can You with Mk IV. Your Heavy Attack (You'll most likely be using the first one with the rev) has a very short but noticable windup which CANNOT be sped up with attack speed... while Heavy Attacks from Mk IV does not possess such a downgrade...) and in combination with rev taking 1 extra shredding tick time it makes it worse overall than the other option - on paper it does more damage yes however in practice when You will be fighting multiple enemies You might not be able to finish revving due to being potentially hit/dodging away from an overhead which in turn makes You lose the damage potential of it
6. Perk and Blessing choices are important:
- +25% damage againts Carapace and Unyielding maximizes damage againts the most beefy targets; it is better to amplify the damage on those specific health bar types (not to mention Maulers, Plasma Gunners and Twins heads aswell as Scab Ragers torso)
- Bloodletter blessing is not considered by many to be worth picking but... its 14 stacks of bleed on a rev on a press of a button - why ppl take Puncture on Bolt Pistol but don't apply the same logic on Chainsword/Chainaxe is mindboggling to me... It helps in dealing with beefier targets and if You cannot finish Your rev for whatever reason as long as You deal 1 tick of damage with the rev You will apply those bleed stacks upon the enemy which generates damage that might finish off the target if its already injured
- Wrath blessing despite being nerfed to lose all stacks upon missing is still better than Savage Sweep or Devastating Strike if You need cleave... and You will need it
People were pointing out that lack of Shred is bad; cleave IMO is more important and it shows when fighting huge masses. Another blessing not included is Rampage; despite the description stating it increases damage it infact increases Power; 36% bonus however is still not good enough to be considered better than Wrath. Cleave is much better than damage in this situation cause more enemies hit = enemies get staggered = enemies stop attacking
7. Some people stated that Engage augment for Break the Line is and I quote;
'The extended range on BTL is a bait talent for noobs that gives you almost nothing of value'
'All that talent does is mean you run an extra 3.75m if there's nothing in front of you when you activate the ability'
'Any elite or sufficiently large horde in front of you means you'll stop short anyway, and thus get no value from the talent'
Yeah... about that... there are many situations where that extra range allows You for quick repositioning, engagement with enemies pestering teammates and stopping them from attacking and/or engaging specials behind Chaf which would normally block You from reaching; 'sufficiently large horde' will never stop Your charge. Only Specials, Elites and Bosses will - You phase through everything else with no collision!

Thats about it! It is by no means a meta build nor great weapon but its good despite its limitations... and satisfying to make generally considered weak weapons perfectly viable... if not better than general choices in some areas!