Looking at their melee attack, 1d10+3, that means their biggest theoretical damage roll is 13. A Marine's standard resistance is 12. So that means in order to actually wound the marines, you have to roll max?

Or can even non-Astartes characters confirm Righteous Fury?

Howdy!

Hordes add 1d10 to their damage for each tens digit of their magnitude up to an additional 2d10 damage. No rightous fury for hordes. So for example 1d10+3 becomes 3d10+3 for a magnitude 20+ horde. So actually it could do 33 damage before armor and TO of the Space Marine. Ouch.

Just quite how they all manage to attack at once might be an interesting question...

Kage