Ogryn Bullrush Heavy Hitter Knife
 Ogryn Build - Warhammer 40k: Darktide 

On bullrush you really really want for the lil uns. Being able to charge across the map and pick up an ally instantly will save runs more often than doing the most damage. Slam also gives you stamina, which is invaluable if you run into a situation where you need it and have to keep dodging. Which will be half the game because you're the ogryn. Consider dropping some damage reduction and picking it up once you're comfortable surviving on higher difficulties without it.

Don't need all the bullrush talents. The damage against stunned is actually good if you weave in punches to interrupt over heads and open up shields, and the mkiv can stun ogryns, so keep that honestly. Because you should be using punches I'd even suggest taking tenderiser. Your single target should open with punch > heavy light light. All three of those will get the 30% strength. Good for bosses too. Can kill a crusher in 2 combos on auric if you have the rending after elite kill. Doubles as a little bit of extra cleave and makes the damage from furious redundant so frees up a talent. For hordes Punch > push attack > heavy > light. Or Push attack > light > light > heavy depending on the situation.

With impactful you can knock maulers over, with the cleave you do more horde clear. That one's up to you.

It depends on how much you can afford to prioritise damage as to whether you want to keep payback time and furious, but I would seriously suggest dropping them in favour of regen while bracing and for the lil uns. The rending and damage against stunned though are too good for the knife, and imo not worth dropping for damage resistance, unless you're struggling to stay alive.