current fav vet build
 Veteran Build - Warhammer 40k: Darktide 

Weapons: Maccabian Mk IV Duelling Sword and Accatran Mk XII Recon Lasgun are my go to's; both have high mobility and can deal with many enemy types. 

• I just choose DS because it's too good not to pass up lol. I put on Carapace and Flak damage to cover most of the enemies that the lasgun isn't dealing with. Thrust is to help deal with bigger health pools (consider using Riposte / Precognition instead) and Uncanny Strike because it's good for anything. 
• For lasgun, Unyielding and Infernus is to melt bosses, and crit chance and Headhunter is for ammo efficiency. 

Curios:

• blessings/main stat: stamina (since your melee isn't as good, you'll need to be creative with blocking and pushing hordes), toughness x2
• perks: CDR, toughness, stamina regen (consider changing 1 stamina regen to a block cost efficiency)

Talents:

• top: Out for Blood is more consistent than Confirmed Kill ; lets you regen more on, say, hordes and is the obvious choice when elite-starved
  • (I've been debating the effectiveness of the middle nodes vs the right-side nodes for a long time, the choice isn't as obvious as it is for plasma gun and havoc has a lot of elites so feel free to experiment)
• blitz: Shredder Frag Grenade is amazing CC/horde clear, remember to throw 1 whenever you have 2+
• aura: Survivalist + Catch a Breath are just "do what you do and profit" nodes
• ability: Demolition Stockpile + Voice of Command ("shout") are no-brainer BIS options for vet
• left tree: 
  • Precision Strikes since you should be aiming for heads anyway (Headhunter blessing)
  • Shock Trooper : self-explanatory, the holy grail of the lasgun
  • (not taking Superiority Complex here and having Focus Target make up for it, since the keystone is more versatile)
• middle tree:
  • Born Leader to help with ally toughness regen; the nodes next to it don't seem as good (maybe if For the Emperor! was longer?)
  • Iron Will gives insane TDR, works with gold toughness since it's over 100%
  • Demolition Team for more shredders, which will get much more value as difficulty goes up
  • Bring it Down! because you always need more boss damage (Rending Strikes is just so insignificant)
  • KEYSTONE: Focus Target! to help with bosses and basically anything else, you can just tag someone and let your team go ham on the enemy while you shoot something else
    • (consider dropping Superiority Complex and Bring It Down to take Weapons Specialist + On Your Toes for more survivability + Zealot-comparable melee speeds, the only downside being that it doesn't synergize as well w/ recon lasgun as it does for plasma gun)
• right tree:
  • Reciprocity , also a "do what you do and profit" node
  • Desperado because it's just free stats to your melee, which is sorely lacking without this node
  • Trench Fighter Drill to further push melee stats

Overall:

As mentioned, this is an off-meta alternative to plasma gun (which may get nerfed lol). Unfortunately, using it will make games quite difficult for little damage in return since Vet is a squishy class and you can't get much better than plasma gun/DS4, so it will be hard to get value out of this build compared to just playing other builds/classes. The hope is that your team-wide ammo efficiency, flexibility, and ranged support will make up for it. Plus, you get to hear the BRRRT of the lasgun all game, which is fun :))

PS: This build should be considered an ongoing WIP, since I haven't made it to h40 yet (highest completed was h35 and I got carried ALL game) and I'm still figuring out what works best for highest difficulty situations without accounting for raw player skill. Plus, there aren't a lot of good recon lasgun resources out there besides other builds on this website so it's hard to say what the "meta" is for this off-meta playstyle.