Hati
Inside his helmet, Hati grins. About time they showed up, this mission was looking like it might end up being quiet and boring the entire way through. He whirls, leveling his Storm Bolter at the northern horde, thumbing the fire selector to select the Metal Storm rounds. No sense in wasting the Hellfire rounds this early in the mission.
He laughs merrily as he depresses the trigger, letting loose a storm of metal and explosives accompanied by the droning roar of his weapon. "Hah, Brothers, I don't think this lot will last very long" he laughs over the Vox, "Shall we make it a competition? Most Tyranids felled this day, or something along those lines?".
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Hati fires a Full Auto burst from his Storm Bolter with Metal Storm rounds at the northern Horde.
BS is 50(Base)+5(Armour)+20(Auto-Fire)+30(Massive Horde).
Ballistic Skill 105: (1d100)[34](34)
No need to roll for damage, as he also automatically deals damage to Hormagaunts.
Storm doubles the number of hits, as does Metal Storm rounds. Which means he's getting 4 hits per degree of success, if I'm understanding the rules correctly. Plus 1 for the Explosive damage type.
EDIT Seven degrees of success then, but the RoF on the Storm Bolter is only 4, so 4 hits. Plus 1 for Explosive, double that for Storm, then double it again for Blast (2). Total of 20 Magnitude damage.