Optimized Dakka build based on Siuns
 Ogryn Build - Warhammer 40k: Darktide 

Why this build?

The Twin-Linked Heavy Stubbers (TLHS) are absurdly powerful ranged weapons thanks to their insane damage against most targets, even Crushers, if used with Point-Blank Barrage and with the correct talents. They are also very fun. However, they have one major drawback and one minor. The major issue is that it uses up absurd amounts of ammo and makes it very easy to constantly run out of ammo in a very short time. This requires the Ogryn player to steal all the ammo all the time, which of course is horrible for team play. The minor drawback is the poor accuracy on longer ranges. I would say that it is a major one as well, but this one feels like a natural way to balance the weapon (in the way that is the same for the Inferno Staff) while the ammo one is sort of a "this makes it unusable" issue. You also have The Rock™ for longer ranges, even if it is fairly difficult to hit at longer ranges. How do we fix the ammo issue?

Only shoot the TLHS (ideally at 12m and below) with the ultimate and stop firing once the ult is over.

The explanation is simple - we use the last effect of Point-Blank Barrage, which is regaining 50% of the spent ammo upon the end of the ultimate. This and Burst Limiter Override (which we can't adjust to via playstyle) are the only talents of the Ogryn that allows them to regain ammo or conserve it. The entire build is set up to play around that aspect. Hit enemies with the Power Maul until you see a good opening to use the ultimate, use it, shoot until the ult is off and immediately go back to your Power Maul. 

If you want to brace the weapon, swap to the TLHS first, start bracing, then press the button. 

Otherwise you will use a good chunk of the 12s just to brace the gun. This also makes it necessary to at least leave 1 shot in the weapon when swapping away from it, otherwise you cannot brace the weapon when swapping to it again without reloading. Alternatively, use the Mk VII TLHS (see below).

Explanation for the TLHS weapon variants:

• Looking at the average damage value and multiplying it with the total ammo count to obtain the "total damage possible for the ammo" value, all three of them are very similar with the order being Mk V > Mk IV > Mk VII, with a ~8% drop from Mk V to Mk VII
• Gorgonum Mk IV Twin-Linked Heavy Stubber provides the best Carapace damage slightly outperforming the others with the ult activated. It also has the highest "far" range (but see the notes on the Mk V as well). It can also be controlled pretty well in both hip fire and braced in my opinion.
• For some reason it is affected by 60% stability increasing its weapon spread if stability is chosen as the dump stat. This will result in it having the highest spread, which isn't that big of a deal for close range but not great for mid to long range
• Achlys Mk VII Twin-Linked Heavy Stubber the best fire rate, least overkill potential in theory (not in practice) and best synergy with Bullet Bravado, but the least range and hip fire recoil is massive.
• Importantly, it also takes the least amount of time to go into braced mode as it can be fired earlier than the animation makes it look, which isn't true for the others (might be a bug?). This actually allows a more fluent play style of switching with the ult and going into the braced stance quicker.
• Krourk Mk V Twin-Linked Heavy Stubber is the middle of both, but with the shortest "near" range (11.4m) and the hip fire control also being quite rough.
• (Unclear as I couldn't find an explanation for this mechanic) It seems to be the one that has the best damage drop off with range in the mid-long range department. At least it is the only one of them that has a 0.99 multiplier at 80% range for unarmored and maniacs at far range. But I'm not sure if the lower % with the Mk IV means that it also has 0.99 multiplier at the same ABSOLUTE range (37m) while it only drops when farther than that (i.e. between 37m and 54m). If the latter is true, this weapon doesn't really excel at anything, if the former is true, the weapon is better at killing Unarmored, Unyielding and Maniacs in the range between 12m and 37m. Flak Armoured and Infested enemies remain the same.

I would probably either go with the Gorgonum Mk IV Twin-Linked Heavy Stubber for its slightly higher damage against armored enemies and great control when hip firing or go with the Achlys Mk VII Twin-Linked Heavy Stubber for its great synergy with Bullet Bravado and to allow for the quicker braced weapon mode when activating the ult. 

In any case we take "+25% Damage against Flak Armor" and "+25% Damage against Carapace Armor" to maximize our damage output against the enemies the gun is the weakest against and because it actually allows the guns to kill Crushers very quickly (~6000 dps with fully stacked Blaze Away and Fire Frenzy). 

Explanation for the talent and Blessing choices above

• Bruiser paired with the "+4% Combat Ability Regeneration" and Maximum Firepower is very important to keep the CD of Point-Blank Barrage (60s base) as low as possible and to have it available whenever we want to go for Dakka (or need to)
• Fire Frenzy and Blaze Away in unison especially make the TLHS do truly absurd amounts of damage once they are stacked up. Fire Frenzy is a bit harder to trigger (12m range) but if you do, it is very powerful. It also synergizes well with the +15% Close Range damage from the ult and all the "on kill" talents that the build has, namely Massacre Dominate and Burst Limiter Override . 
• The build doesn't take Charmed Reload because the way the magazine size and fire rate of the TLHS' are currently set up, all of them are able to fire for around 12s at 80% ammo - precisely the time that our ult is active for. Since we want to stop firing right afterwards, Charmed Reload wouldn't do anything in this build and play style. 
• The rending provided by Dominate and Hail of Fire massively increases the damage against armored targets.
• Achlys Mk I Power Maul is the perfect sidearm because of the special attack "burst" and stagger it provides. Swap to it, use the special attack, hit people, usually a second special attack for stagger which allows for a safe transition into Point-Blank Barrage, which should be ready by the time the second special attack has been performed, especially if the special attacks killed an Elite and triggered Bruiser. Power Surge allows it to deal very high damage to Crushers and oneshotting pretty much any other armored target, which is ideal in this build as the TLHS uses up a lot ammo for Crushers (unless fully stacked). Also increases the stagger radius and makes horde killing possible if you trigger the effect. Skullcrusher because its effect is one of the biggest damage increases in the game and the Ogryn does very high stagger. Dominate is also very easy to trigger with the special attack and Massacre is also neat as the Power Maul has quite a high critical multiplier, especially when missing the weakspot. 
• The build takes Bonebreaker's Aura Strike True Batter Melee Damage Boost Slam The Best Defence Frenzied Blows as talents as this is a "hybrid" build meaning you also do a lot of melee combat. These talents provide some of the most important Ogryn melee combat related talents that we can afford to take. It takes Bonebreaker's Aura instead of Coward Culling to provide an IMO much better aura to the team. 
• Big Friendly Rock is used for single specialists and longer ranged ones so you do not use up your ultimate or ammo for them
• A total of three Toughness Boost paired with 3x Toughness Curios gives a very good amount of Toughness
• Steady Grip Bullet Bravado Can't Hit Me...Again and Mobile Emplacement with all that Toughness makes this build tank damage incredibly well during the ult, especially against ranged enemies.
• Bulletstorm over Heat of Battle as the former increases our total damage we can do with our ammo, while the latter increases our damage by using it up faster, which isn't the goal. The former essentially provides virtually more ammo (or more total damage for our ammo). 
• This build does NOT take Concentrate as we ideally fire at close range, where it isn't needed and because it removes stamina, which can be bad once we leave the braced stance. 

Alternatives

• The Best Defence instead of Smash 'Em! or Steady Grip (as the latter situation is already stacked). I think exchanging the latter is especially sensible if the Mk VII TLHS is used as that one provides a ton of toughness with the ult already.
• Lucky Streak - The way I understand this talent it works by increasing the ADDITIONAL damage your crit would do by 75%. E.g. if your hit from a Mk IV against a Carapace Armor damage would do 61 normally and 79 with a crit, it increases these additional 18 damage by 75%, resulting in an increase to 92,5 damage from 79 damage (~17%). That is a good value and synergizes well with Good Shootin' and Massacre resulting it in being triggered pretty frequently, but it still provides less consistent value than Dominate especially against armored enemies (which are the bigger problem for this build). 

Tips for gameplay:

• Obviously it can be important to also shoot outside of your ult, especially when a dangerous special is coming and there are no Rocks available for example or when there is an abundance of ammo and you can just shoot anyway
• Killing 2-5 smaller enemies like Poxwalkers before or at the beginning of a ult is a good idea before you switch to the main targets (e.g. Crushers or Scab Ragers) as it massively increases the damage thanks to Massacre Dominate and Burst Limiter Override 
• Judging when to use the ult has a bit of a learning curve