Anti-Elite Bolter - Havoc 35+
 Veteran Build - Warhammer 40k: Darktide 

Designed around hitting breakpoints on elites in high havocs. The build's major deviation from meta Focus Target! talent setups is investing in Kill Zone on the lower left side of the tree for more reliable breakpoints.

The combination of 6 stacks of Redirect Fire! , at least 2-3 Focus Target! stacks, a few Pinning Fire stacks, Longshot , and Kill Zone (not to mention bleed stacks from Puncture ) end up hitting a lot of one-shot breakpoints on ranged elites and specials without having to rely on crits.

This build is inherently less versatile / has less solo-carry potential than dueling sword plasma meta builds, but provides exceptionally low TTK on priority targets and higher boss burst potential without sacrificing shout or focus fire. It fills a niche similar to Helbore builds, but with stronger defensive and burst characteristics.

Ranged Weapon

• Why Mk Locke Mk IIb Spearhead Boltgun over Locke Mk III Spearhead Boltgun ? Ammo efficiency (more single-target damage per bullet and more ammo capacity), ability to burst bosses with weakspot hits in panics, and has cleave to kill snipers / bombers etc mixed into hordes (Mk III always detonates on the first target hit). The Mk III is superior for dealing with groups of regular shooters, but on balance I don't think it's worth it since if you have the rhythm of scope -> single-fire -> unscope before recoil fully registers -> re-scope you can get decent clearing capability without sacrificing the cleave needed to delete specials that can wipe a team.

• Why bolter over plasma? More ammo efficient if you hit headshots, lower TTK on particularly dangerous enemies like reapers, a little more flexibility in situations involving surprise armor or bosses, lower TTK for shooter removal (higher ROF lets you retarget faster), better movement characteristics, equivalent or better capacity for burst damage and stagger in panic situations (tapping m1 to shred or stagger a rager/bruiser/mauler clump can save you, special action can push bursters and stagger scab ragers on weakspot)

  - Notable weaknesses vs plasma - reduced cleave / no wallbangs, cannot stagger muties/crushers/captains with headshots.

• Why bolter over Helbore? More capacity to quickly burst or solo bosses in emergencies, equivalent or better cleave, better movement characteristics, no reliance on stamina/crits for hitting breakpoints (can keep a health or third toughness curio instead of a stamina curio), better performance in panic situations

  - Weaknesses vs Helbore - much less ammo efficient, no huge instant brittleness team utility from Armourbane , no bayonet for captain shields, worse performance against crushers and maulers

Blessings

• Pinning Fire will almost always have at least 2 stacks due to sheer density of enemies, extremely useful for breakpoints
• Puncture helps with ammo efficiency / if you miss headshots on scab gunners while missing some kind of stacks; helps reduce cognitive overhead and retarget faster
• Shattering Impact generally not worth it since you're trying to one or two-shot your primary targets. Builds like Rumbler Ogryn and arc Skitarii apply brittleness much more effectively. Kraks are generally the better option for armor packs, and your melee should be able to handle isolated armor. For unyielding bosses you should be leaning on kraks + max focus target stacks. Power or Dueling swords can help finish them quickly.

Perks 

• +Flak is non-negotiable - needed to reliably kill scab gunners and helps kill plasma gunners
• +Elites makes headshots basically always one shot kill on scab gunners. +Unyielding doesn't change breakpoints on reapers. With or without, they're two-shot headshots or one headshot one bodyshot
• If team lacks answers for quickly deleting twins, can take +Carapace to allow for one-phasing Rinda. Otherwise not as useful as +Elite consistency imo - helps if you need to panic clear some crushers or maulers, but kraks are generally better suited for armor packs anyways. With plasma gunner and mauler headshots you'll get equivalent TTK by hitting flak bodyshots and for scab ragers you should always be going for headshots

Blitz and Talents

• Taking Krak Grenade lets you preserve your bolter ammo for elites/specials. Use grenades liberally against armor packs and bosses.
• Very few talents can get moved around here if you want to keep the necessary 6 redirect fire stacks, Kill Zone, and elite damage earlier in the tree. 
• Volley Adept is basically required for Bolter - its's the single biggest reload buff you can get and you'll have 90%+ uptime. Further reload nodes or a +reload perk on the bolter aren't worth it imo. Just practice cancelling the reload animation right when the final sound cue starts when pulling back the slide (to see exactly when, watch when your ammo counter changes from 0 to 15) - cancelling with a sprint is fastest, but the push special action is only a tiny bit slower than a sprint cancel and lets you dodge immediately. You can buffer ADS out of special action, too.
• One Motion is theoretically optional if your awareness is cracked enough, but in practice it's very helpful since you'll want to have your melee weapon out for mobility most of the time, and that accelerated draw time will absolutely help you catch snipers and bombers. You can always shout to cancel the draw animation, but it's best to keep that capability for emergencies imo since instant gold health + kb + revive is a critical team resource.
• Only In Death Does Duty End is also theoretically optional - I used to run the white 15% melee damage boost node instead, which helps with poking twins in the head and for a few useful breakpoints. In practice, revive shout utility seems like too much to pass up and you can horde-clear defensively without the extra damage.

Melee Weapon

This build lacks nodes enhancing melee damage, so there are compromises here.

Achlys Mk VI Power Sword with Slaughterer is the best way to kill chaff while keeping capacity to chunk armor and bosses. +Carapace will let you kill crushers and maulers quickly without spending resources, and will help you do meaningful damage to twins. +Unyielding is also helpful for bosses and bulwarks in particular. 

However, the combination or mediocre runspeed and dodges, and vulnerability during activation window (mitigated only by freezing stamina regen for sliding activations) make you less capable of clutching rescues or revives when shout is on cooldown.

Other options depending on team comp and personal preference:

• If team lacks a source of Skullcrusher  and/or very high single-target to skip captain phases, take Shock Maul. The special attack will chunk captain shields and make their fights go quicker. I prefer the Munitorum Mk III Shock Maul.
  • Skullcrusher and +Maniac is non-negotiable (dreg ragers are your nemesis and muties take a couple of weakspot hit to kill)
  • I generally prefer Hammerblow and +Unarmored for safety and horde clear (+Unarmored helps with groaners, traitor moebian and scab bruiser weakspots. +flak doesn't seem to hit valuable breakpoints e.g. dreg bruisers). Munitorum Mk III Shock Maul H1 -> L1 loop will keep you safe and prevent you from getting tripped by unkilled chaff
  • Alternative setup more ability to kill armor in a pinch - High Voltage and +Carapace. Doesn't kill/ knock back chaff as well though
  • Extra dodge and block efficiency relative to powersword helps with survivability, but maintains mediocre runspeed
  • Stunning crushers and unshielded captains with special action is extremely funny but requires forethought and usually isn't worth it
• If you struggle to survive with powersword and want to prioritize mobility / staying alive and to better stall for shout revives, take a pokey dueling sword  - can't go wrong with Maccabian Mk IV Duelling Sword 
  • Suggest Thrust (for poking muties) and Uncanny Strike  (you'll want the on-demand brittleness for armor). Without melee damage or crit nodes you won't be getting much benefit out of Riposte . Agile is neat but dueling sword already has plenty of dodges and extra melee damage is very much welcome on this build
  • +Carapace and +Unyielding for efficient armor removal and boss contribution
  • Dump cleave damage for mobility
  • Rely on your movement attributes and parry to avoid getting bogged down. Getting isolated and bodyblocked by chaff is your biggest threat.

I generally find power falchions underwhelming without extra damage nodes, and it lacks the utility of shock maul, but it might be worth a try. 

Synergies

• Works very well with anything that applies brittleness to further enhance your boss damage - e.g. Lorenz Mk VI Rumbler Ogryn, arc Skitarii.
• Has exceptional synergy with other veterans - the Fire Team aura helps hit breakpoints even more comfortably / gives you more room to bodyshot. Plasma's biggest advantage relative to bolter is its increased cleave / greater reliability killing enemies in cover or behind walls, so having a plasma vet can plug holes in bolter's coverage. Taking kraks also frees the other vet to take smokes or frags which each have great team utility.
• Horde-control specialists - e.g. Rifthaven Mk II Inferno Force Staff or Equinox Mk III Voidblast Force Staff or greatsword psykers, taunt ogryn, relic blade zealot etc - help keep space open for you to focus on distant threats.
• Works well with the Dog Whistle mod. I suggest auto-targeting: bombers, snipers, dreg/scab/plasma gunners, reapers, and Rinda Karnak / melee twin (tracking her quickly is hugely helpful). Flamers and trappers are okay to include but are usually easier to spot due to their aggressive movement. Set auto target cooldown minimum to 2 or 3 seconds to balance having healthy focus fire stacks and quickly identifying priority targets (setting the focus fire restriction instead of by time exhibits some inconsistent behavior, esp when there are multiple focus fire vets on a team). I also recommend having an easily accessible toggle bind for when you want to ensure you keep 6 stacks on a boss (I use the grave/tilde key).

Similar Builds

• [META] NRGaa's Bolter Veteran Havoc 40: Very similar concept, but sacrifices Focus Target team utility and some survivability in exchange for more even more consistent breakpoints and better melee performance. A good read - the positioning, blitz usage, and enemy prioritization guidance there applies to this build.
•  Two Tapper by ripthejack3r: Similar concept and almost identical talents, but uses the Mk III and some slightly different outlook wrt weapon setups.