Infinite Infantry Lasgun
 Veteran Build - Warhammer 40k: Darktide 

Kantrael Mk IIb Infantry Lasgun is against everything what's not Carapace armored.
Pair Deadshot with Executioner's Stance as much as you can, since after recent patch, Mk IIb variant now has much lower recoil, and Deadshot with Executioner's Stance allows us to spam shots with pin-point accuracy like Accatran MG Mk II Heavy Laspistol.
Withering Fire allows to penetrate one more smaller target, which will proc Headhunter and Tunnel Vision twice per shot.

So much stamina related talents was picked because Lasgun shoots fast + I find it the most comfortable in terms of general use. Otherwise I have to always look after myself, for example, not sprinting too much, or trying to proc Duck and Dive outside Ghost, etc.
Sprint efficiency was taken because we're spending a lot of time sprinting and stamina is crucial for us. 

Using Exhilarating Takedown solely because of additional toughness damage reduction for our CQC moments. It'll last about 24s if we count all 3 stacks. We already are pretty low on toughness (172 when I usually prefer around 200), which makes Iron Will less effective (works on 43 instead of 49-53, and keep in mind this is even lower on Havoc 40), but if you don't feel like this is a problem for you, switch to Out for Blood.

Krak Grenade oneshots Havoc 40 Crusher.