Murder Lead (Combat Blade) Crit
 Veteran Build - Warhammer 40k: Darktide 

Update : Switched "Always Prepared" for "Field Improvisation", because on the hardest levels, this can turn everything around, and I end up personally reloading my weapon manually.  Oh and people will love you for it.

A combination of one of my favorite builds (squad lead) and any of the older combat knife builds for veteran.

This is an all around build, best used with a fast weapon (knife) that can do a higher quantity of critical hits (knife).  Ranged slot should be something you feel comfortable killing specialists with.

With this build you have a get out of jail free card (Voice of Command) with Iron Will (50% reduced toughness damage if above 75% toughness) that will let you take some solid hits if you make a mistake.  Kill a specialist and reduce the cool-down by 6 seconds!

Voice of Command should be used regularly, and almost always on cool-down.  It can be used to assist in reviving, stop a charge of crushers, etc.

Throwing your grenades should happen regularly, you are carrying 3 krak grenades and they replenish every 60 seconds.  Avoid picking up grenades if your teammates need them.

Nodes that are selected that can be removed (especially if you want to assist your group more)

Always Prepared - Reloads 3.3% of your ranged weapon magazine when you switch to it per melee kill (up to 10)

Grenadier - +1 extra grenade

Onslaught - Apply brittleness per hit

Stamina Regen Boost - .25 second delay reduction

Melee Damage Boost - 10% raw melee damage bonus

Rending Strikes - 10% Rending to ALL weapons (melee and ranged)

With these 6 points you could pick from any of these other things that can be useful (I put them in a general order of usefulness)

Born Leader - Allies get 15% of the toughness you get

Competitive Urge - 2.5% chance of 20% damage bonus, impact bonus, and suppression bonus when anyone kills any enemy (affects ranged as well)

Reciprocity - 5% crit bonus on dodge, stacks 5 times (if you are using something without a higher crit chance)

Inspiring Presence - 10% toughness replenishment for you and allies

Bring it Down - 20% bonus to Ogryns and Monstrosities 

Only in Death does Duty End - Voice of command revive shout, but with some penalties

Serrated Blade - Guaranteed bleed on hit, great with Mercy killer on weapon

Remember that +25 toughness is great, that's 6 extra points that take half damage, so it is technically 31 toughness, but gives you more of a buffer with your regular toughness to stay in that top 25%.

Second blessing on the knife, there are quite a few good ones:

Executor (Power on weak spot hit (repeated), Lacerate (Bleed on non weak hit), Mercy Killer (Extra weak spot damage if target is bleeding), Uncanny (rending on weak spot hit), Ruthless Backstab (High rending on backstab hit)