Bolt Action At Home - Havoc Build
 Veteran Build - Warhammer 40k: Darktide 

Yeah, the Agripinaa Mk VII Combat Shotgun is not a bolt action but is the closest thing DT has to a manually operated long range one shot/headshot anti material rifle. The slugs will one shot, one kill anything that isn't Crusher or Scab Mauler even without most of your damage bonuses and even then Scab Mauler will go down in one if you have Executioner's Stance / your damage perks active. Even if it doesn't kill the target it has enough stagger to send them sprawling or stagger them for lethal follow up shots. Also if the slug hits a bulwark shield it will open up their guard for a follow up headshot. You can unload buckshot or snipe monstrosities with slugs (dps vs. ammo economy and single shot damage) both will deal great damage if you have your buffs up. The only thing the shotgun can't really deal with is hordes which is why I recommend going Shredder Frag Grenade and/or Catachan Mk VII "Devil's Claw" Sword for the horde clear / mobians / rotten armour. One thing to learn is how to maximize your reload perks (always make sure to have at least one shell left in the chamber for that 20% when you reload after unloading into a group of specialists, 55% reload speed makes 17 shells load a lot faster)

Alternate Nodes

Withering Fire I used it recently and honestly I might prefer it to Man-Stopper on the shotgun for that fun cleaving. Not 100% necessary, but fun when you can maximize on it.

Skirmisher Probably the biggest that every single other build with this gun recommends. A node that gets recommended a lot and personally I recommend it if you mostly prefer using buck to the slugs and can manage it next to the reload perks and other damage buffs. Don't get me wrong its a great damage buff but two nodes is a lot for something you might find yourself micromanaging next to Marksman's focus.

Cut-able Nodes

Rending Strikes Chink in their Armour Both rending nodes which make killing carapace a lot easier, with them you can down crushers in 2-3 shots and maulers in 1-2 but yeah cut if you want more pure damage for killing bosses or to second as a grenadier or not to die as fast.

Opening Salvo If you are solely using the buckshot then this node is a lot less desirable, but if you are going that road you might get better results with the Accatran Mk III Huntsman's Shotgun .

Alternate Melee Weapon choices

Yeah the Catachan Mk VII "Devil's Claw" Sword isn't the best melee choice but I think it shores up the main weakness on this build. However if you want something that is better mobility the combat blade, tac axe or dueling sword all work to get you moving faster. Personally I would recommend the Catachan Mk VI Combat Blade as it has sweeps and not bad single target with its push attack. You could also go a heavy sword of any mark for cleaving hordes.

Final Note

Agripinaa Mk VII Combat Shotgun is not an easy weapon to use, it definitely requires a bit more management than the plasma/recon las/boltgun weapons most veteran builds use but when used to its full potential it can match them pound for pound in damage and is quicker to pull out and blast stuff with a reasonable ammo economy.