IAG5 Terminator
 Veteran Build - Warhammer 40k: Darktide 

Intro:

Whoever said "You can achieve anything, but not everything." has not met the Columnus MK V Infantry Autogun on a Veteran. Are there individual guns that can perform slightly better than it? Sure.

• You can instakill almost any non-boss/crusher with a Hellbore, Kantrael, or Vraks MK VII. 
• You can fire for longer stretches with a crit-build Recon Las Gun Mk. 2 with Shock Trooper.
• You can probably one shot any non-boss with a Plasmagun. 
• You could easily clear out a horde and stagger elites with a Shotgun. 
• Point blank a Braced Autogun will do more damage. 

All of these can achieve anything. But the Columnus can achieve everything, and that versatility is better than anything.

• Even though it only does 75 average body damage per shot, it will deal upwards of 250-320 crit weakspot damage before any additional modifiers meaning that any elites you headshot will die.
• It has one of the fastest available reload speeds at 2.54s so you can keep Executioner's Sentence up perpetually without spending talents of % Reload on Elite Kill or Ammo in Magazine. 
• At 13.33/rnd per second the thing is a literal bullet hose and you can spray and pray to clear out hordes. 
• Due to its fast fire rate it will instantly suppress anything you shoot at. 
• You can ADS and take advantange of multiple weakspot kill related talents to improve performance and engage mid-range targets from across a room. 
• With Talents it can have upwards of 57 ammo per magazine and 750+ ammo overall making Survivalist aura return 7 ammo per kill allowing you to have amazing sustainment an entire match even if you're just spraying into poxwalker hordes between specialist/elite packs. 

That is the beauty of this build. It can do 90% of what every other gun can do. It is every gun rolled into one complete package without sacrificing your defensive capabilities.  

Playstyle:

The Columnus shines when it is getting critical strikes and headshots. Thus taking Deadshot drastically improves its overall performance as you ramp up your other bonuses. For this reason I went with a +3 Stamina Curio as Deadshot is extremely Stamina intensive. You also pick up +1 Stamina at the beginning of the middle tree for +4 total Stamina. 

On a defensive level you have the following: 

• Close Order Drill - Up to 33% Toughness Damage Reduction based on Allies in Coherency. 
• Exhilarating Takedown - 15% Toughness and 10% Damage Reduction on Weakspot Kill. Stacks 3 Times. 
• Confirmed Kill - 10% Toughness on Elite Kill and 20% over time. 
• Catch a Breath - Replenish 5% Toughness when 8m from Enemies. 
• Toughness Damage Reduction Nodes - 20% Innate Toughness Damage Reduction. 
• Inspiring Presence - 10% Toughness Replenishment for you/Coherency. 
• Iron Will - 50% Damage Reduction when above 75% Toughness.
• Born leader - 15% of Toughness Replenished is shared with allies on coherency. 

You only have 140 Toughness with this build. But you're getting way more value per point. 

• Additively speaking, Close Order Drill, 3x Exhilarting Takedown, and the Toughness Nodes, give you a whopping 86% Toughness Damage Reduction. Ironwill will reduce the remaining damage by 50% as long as you're above 105 toughness. 
• If you have any additional damage reduction auras from team mates you take next to no toughness damage when in the zone with exhilarating takedown stacked. 
• Any additional damage reduction curios that you decide to stack on top of that will render you basically immune to that damage type. As long as they are 8m away from me, I can facetank gunners all day. I can also survive a Damnation Sniper Shot without taking health damage. 
• Every ranged weakspot kill replenishes 21 toughness, every elite kill replenishes 14 toughness and a further 3/sec for 10 sec. 
• On average, Born Leader will add on another 2/sec to your allies which is a 33% coherency boost to your entire team even though it is kind of mid. 

The only problems you will have will be melee lessers backshotting you and flamers/bombers that immediately kill your Toughness. Outside of melee bleed through and flame one-shotting your toughness, you will almost never run out or lose your toughness for any reason. 

On an offensive level you have the following: 

• Longshot - 20% Extra Damage based on distance. This is a filler talent for exhilarating takedown. The IAG5 has a 50% damage fall off at range so this helps you make more longer shots but it isn't too great otherwise. 
• Killzone - 15% Damage when enemies are not within 8m. Once again, more of a filler talent, but it helps to even out the damage falloff at range. 
• Executioner's Stance - +25% Ranged Damage and +25% Weakspot Damage when activated. 
• Superiority Complex - +15% Damage to Elites. 
• Ranged Damage Nodes - +10% innate damage bonus. 
• Suppression Nodes - +25% and +50% Suppression Dealt for a total of +75% Suppression. 
• DumDum - 30% Close Range Damage Fully Stacked
• Deathspitter - 32.5% Power Fully Stacked. 

Due to the high-bonus critical strike damage of the IAG5 and the +62.5% damage from DumDum and Deathspitter, you don't need as many offensive bonuses and instead should strike a balance between support and defensive talents that suit your playstyle. If one wanted you could swap out Superiority Complex or Precision Strikes, or drop exhilarating takedown to get Bring it Down! and Rending Strikes in the middle tree. 

While this build is very crit and weakspot dependent, I went with Superiority Complex over Precision Strikes to even out the damage to be more consistent. On Damnation:  Weaker specials/elites will die in 3 hits, beefier ones in 5 hits, and Mutants in 10. Precision Strikes doesn't really change this a whole lot especially once DumDum + Deathspitter are stacked. Your only trouble will be the Mauler (No Headshots) and Crusher (All Carapace). You can kill a Mauler in about 20 bodyshot hits, and a full magazine emptied into a crusher's head will do about 90% of its health. With Executioner's Sentence up, everything dies in 2-3 hits, Maulers in 10 bodyshots. Given a fire rate of 13.33/rnds, that is less than 1/4th of a second to kill any elite/specialist, and 3/4 of a second to kill a Mauler. 

This ensures that your damage remains relatively stable from close to medium range and allows you to engage at the 2-3 shot breakpoints. Maniac damage is always relatively high, but you'll notice a 50% damage drop for all other armor types at far distances. 

For Crushers/Bulwarks, you have Demolition Stockpile and Krak Grenades. I tend to conserve my Krak Grenades for Crushers, and will rush up to a Bulwark to bait a melee swing or flank it. If you ADS a Bulwark past its shield you will stagger it 99% of the time and can easily kill it without wasting a grenade. If you're facing Bulwarks with a large horde of other elites or Maulers, I would throw the Krak Grenade. 

For Melee, I use the Antax with a Carapace Modifier. A strong attack will stun a Crusher on hit allowing you to a dance of two stong weakspot melee attacks and then backing off on the Crusher's retaliatory strike. Its special attack while doing little damage will also immediately stun anything you hit it with giving you breathing room. It is also a one-shot kill for almost any regular melee enemy without the need to power-cycle with a power sword.  

Your basic playstyle is to be a few meters behind your team mates in the 8-15m sweetspot from enemies, ADS headshotting gunners/specialists/elites, hipfiring lesser melee enemies, throwing Krak at Carapace, and swapping to your axe to conserve ammo or clear out major hordes. I like to fire in 10 round bursts, go into a quick sprint dodge, and then fire another burst and repeat. As long as you have Exhilarating Takedown stacked and routine elite kills you are basically untouchable. 

When you use Executioner's Sentence you can go into Terminator mode where with enough toughness damage reduction stacks, you can walk around ADS Headshotting every gunner in the room with impunity. 

Recommendations:

Feel free to swap out the curios for whatever else you want. If you wanted to be more offensively aggressive then Stamina Regen + Stamina Curios would allow you to run & gun & crit spam to your hearts content. The basic curios here probably go overboard on Gunner/Sniper defense. 

You should 100% invest in the weapon customization mod for the reflex sight. The basic ironsights are absolute garbage but with a good reflex sight the IAG5 turns into a headshot beast. I also like to run the Laser Pointer as it makes me more intuitive when hip-firing but running a flashlight is probably better and less of a placebo. 

As Deathspitter takes time to stack due to close range kills, you could opt to go for Fire Frenzy or even Raking Fire instead. 

If your team has a dedicated Boss/Carapace killer, you could forego Demolition Stockpile and Krak Grenades and just stack more overall flat damage %. 

If you play less aggressively and more defensively than you can probably drop long-shot + exhilarating takedown or some of the other defensive talents to focus on more support/offense. 

If you play with an Ogryn the +20% Damage on suppressed enemies is just silly. 

Having a Zealot with +15% Toughness Damage Reduction is also really good.