Ironhelm Mk IV Thunder Hammer & Kantrael Mk IX Combat Shotgun
 Zealot Build - Warhammer 40k: Darktide 

The way to use this build is simple.  Use your Ironhelm Mk IV Thunder Hammer to take out tougher threats: Monstrosities & Elites (Crusher, Bulwark, Reaper, Scab Mauler & Mutants) and use the Kantrael Mk IX Combat Shotgun (normal round) to snipe specialists (Gunners, Shotgunners, Ragers, Flamers, Bomber & Pox Hound). 

For Horde-clear the Ironhelm Mk IV Thunder Hammer isn't the best, therefore use the Kantrael Mk IX Combat Shotgun and both the normal & it's special round  to thin out the horde before going in with your Thunderhammer.  Be conscious of the limited ammo supply for the Shotgun and try not to waste the rounds against small groups of enemies (use your Thunderhammer for smaller groups).  

• The perks for the Ironhelm Mk IV Thunder Hammer are optimized to assist killing the tougher Specials/Monstrosities (Maniac & Unyielding).  For the blessings Thrust & Slaughterer are the best however if you cannot get Slaughterer then a good alternative is Headtaker. (Headtaker stacks will proc of your Stun Grenade & Shotgun (special round) ticks, making stacks easier to acquire). If you are struggling with keeping your Toughness up, changing to a more defensive set-up with Momentum in exchange for Headtaker or Slaughterer is a option (you will get better with practice).  For the Thunderhammer you want 80% Damage, 80% First Target, 80% Penetration, 80% Crowd Control with your dump stat being Defences with stat priority in that order with Thrust being your priority blessing.

• The perks for your Kantrael Mk IX Combat Shotgun are optimized to snipe specialists (Flak-Armoured & Maniac), however changing your perks to (Flak-Armoured & Unarmoured / Infested) is also an option and is optimized for killing Hordes.  For the blessings you will want No Respite & Full Bore (special sniping optimized), however you may prefer Fire Frenzy & Full Bore (Horde-clear optimized).  If you cannot get Fire Frenzy then Deathspitter is a good option and arguably it's equal.  For the Shotgun you want 80% Damage, 80% Stopping Power, 80% Stability, 80% Ammo with Mobility being your dump stat with a minimum of 51% with stat priority in that order with No Respite being your priority blessing.

DISCLAIMER:  This build is designed with the idea that you have god-rolled these items with TIER IV Blessings and such any information given is based on the predication you have said god-rolled items.  Naturally if you do not have god-rolled items, your performance with this set-up with vary however you should still utilise this build as a template even with sub-optimal gear.