Executioner's Gaze - Guardsman Psyker
 Psyker Build - Warhammer 40k: Darktide 

This isn't a Havoc build. This is just a really fun build gun psyker build; the idea being what if a Cadian shocktrooper was a space wizard. I've had successful games in Auric Maelstrom, but I haven't really played above that since I haven't played really played Havoc recently.

With that said, for the Guardsman theme you want the Infantry Lasgun, preferrably the Mark VII. But I think any lasgun, or any ranged weapon that can snipe, can work with this build. Some alternatives you can roll with could be the Agripinaa shotgun, the Vigilant autogun, etc. Since this build is intended for the Infantry Lasgun, I recommend the blessings Infernus and Deadly Accurate. Most people select Headhunter when making lasgun builds, but I went with Infernus since you're going to crit a lot on this build anyways and the burn stacks from Infernus are great for boss damage.

For the melee weapon, I went with Obscurus Force Sword since it's pretty versatile. You got horde clear and single target combos, and can do both very well. Uncanny Strike and Slaughterer make it easy to clear mixed Carapace hordes. It's honestly not a bad weapon at all once you learn the move set.

Lastly, Disrupt Destiny. This keystone is basically Executioner's Stance. Just shoot the highlighted enemies and you'll be getting bonus damage on your crits and weakspot hits; this includes your ranged weapon.

That's pretty much it. Have fun and enjoy   o7