Elysian Helldiver
 Veteran Build - Warhammer 40k: Darktide 

This build is entirely focussed around my favourite gun in the game, the Accatran Recon, specially the Mark 6d variant. In order to get the most of this gun, we focus on stacking crit chance to take advantage of the Recons blinding rate of fire, giving us constant crits. We then combo that with Shock Trooper to allow us to keep up the pressure without burning through our ammo reserves and Infernus to deal even more damage. In addition, we stack Brittleness and Rending so we can melt through armour. It's not meta, and I've yet to try this build on Damnation or beyond yet, but it's a lot of fun.

Talents

There's a bit of flexibility in the talent picks for this build, with the top half of the tree largely being up to your own preferences. That said, the best talents are arguably at the bottom of the tree, so I recommend spending no more talent points than necessary to past the ability talents. Below I'll detail only the talents I consider key to this build; all other picks in the tree above are largely my own preference.

• Shredder Frag Grenade - Useful against unarmoured elites and monstrosities, as well as particularly dense blobs. Krak Grenade, while good, requires you to either burn another talent point or skip out on Survivalist, and ultimately our gun can handle the kind of threats kraks are built to counter. Keep in mind there are no  grenade regen talents in this build, so make each one count.
• Survivalist - The Recon burns through ammo, so we need all the help we can get to stay on top of it.
• Opening Salvo - Given that this is a crit focused build, anything that boosts crit chance is important. Combine with reload speed reductions to enable you to trigger this more often.
• Executioners Stance - A nice little damage boost, trigger it regularly when going up against groups of elites, specials or a boss.
• Deadshot - Hugely important, giving us a massive 25% crit chance boost while aiming, at the cost of stamina. It's important you keep this in mind during play; conserve your Stamina by sprinting only when necessary and hipfiring at chaff; only use ADS for priority targets, and do so in short bursts. I recommend taking any bonuses you can to stamina capacity or regen rate.
• Shock Trooper - Another really important talent, this allows us to convert our crits into ammo, which massively offsets the recons habit of burning through ammo. In a strange and understated way, this talent syergises nicely with Opening Salvo, not only benefitting from the increased Crit Chance, but extending it's window by reducing ammo use.
• Rending Strikes - Grants us access to Focus Target! and gives us rending, which is particularly noticeable on fast fire rate weapons like the recon. This is not the only way to get rending; if you prefer the Marksmans Focus keystone talent and feel confident you can make the most of it, it might be worth saving some talent points and taking Chink in their Armour instead.
• Focus Target! - My preferred keystone talent for this build, as it does not require you to stay motionless, nor use your melee weapon (which this build does little for). Simply keybind Tag to your fire key and forget about it. I've taken Redirect Fire! as my follow up talent, but Target Down! is good too.
• Reciprocity - Another boost to our crit chance; keep up those dodges!
• Onslaught - Another key part of this build, Onslaught stacks Brittleness (which is basically Rending) on enemies with repeated attacks; given the sheer rate of fire from the Recon, we can hit max stacks very quickly and melt through armoured targets with focused fire on weakpoints. Note that the stacks reset if you switch target, so take it one bad guy at a time.

All the other talents not mentioned here do in some way feed into this build, by boosting

• damage
• reload speed for Opening Salvo
• stamina for Deadshot
• suppression, to take further advantage of the Recons considerable rate of fire
• general survivability

Weapons

Your melee weapon is very much up to you, but keep in mind it won't benefit from many of the talents in this build, except for Rending Strikes and Onslaught. You should be using your gun as much as possible, which means your melee weapon will mostly be used for handling hordes and melee elites. 

• Chainsword - High damage and good all rounder. Has rending which can apply bleed stacks and give you some extra crunch on carapace armour.
• Catachan Blade - Fast attack rate, very good at horde clear. Particularly effective against melee opponents due the parry ability, which can mulch Ragers, armoured or not. My personal preference.

As for ranged weapons, it's got to be the Recon. However, which mark? The MkII is outclassed by both the opther marks, which each fit into a bit of a niche:

• Accatran Recon Mk VId - Highest rate of fire, which means you'll be putting out more actual crits, but lower damage which can make getting kills on elites at long range a struggle. Ammo is not much of a concern, but you will eat through slightly more than with the Mk 7. This effectively plays like an SMG, but with the ammo count of an LMG.
• Accatran Recon Mk VIIa - Lower rate of fire, but practically double the damage per shot, which leads to an overall increase in base DPS. Compared to the Mark 6, you should see a higher crit percentage, but the lower RoF does impact the actual number of crits you'll be putting out, which in turn impacts Infernus (and Brittleness). That said, the fire rate is still very high and the higher base damage will make your crits even more impactful. This plays more like an Assault Rifle, or LMG than an SMG.

Speaking of which, the Crit chance perk is also highly recommended, as well as the Headhunter Blessing. Infernus is all but required, as it allows us to get even more out of our steady stream of crits. The last perk is up to you or RNG, though I'd probably recommend damage vs Flak or Carapace.

Curios

Ultimately up to you, but the more bonuses to stamina you have, the more you can use Deadshot and thus, the more crits you'll be dishing out. At minimum, try and get Stamina regen on all three and Stamina capacity on at least one of them.

Recommended Mods

Fatshark, who develop Darktide, officially permit client side mods for their game and as such I personally make good use of them to enhance my experience. Here are a couple of mods I recommend for this build in particular.

• Extended Weapon Customisation - Fun mod that allows you to customise the look of your weapons (to you only), but this mod has a practical impact too; it will allow you to mount one of three sights on any of your weapons. If you dislike the prevalance of iron sights on your guns, I highly recommend this. It also gives you the option of replacing your crosshair with a laser sight, which I personally find useful (and cool). 
• Show Crit Chance - Does what it says on the tin; shows you your current crit chance on your HUD. Useful for getting insight on how much of an impact some of your active talents (Deadshot, Reciprocity, Opening Salvo) have on your crit chance.