He blasted a trio of shots into the side of its face. The bolts were not the standard ammunition of the Adeptus Astartes, but hellfire rounds, created by the alien hunters of the Ordo Xenos. Their explosive cores had been replaced with reservoirs of molecular acid created to react with the tyranid physiology and burn through their chitin and flesh like the flame of a cutting torch. The side of the Swarmlord's face disintegrated, revealing the sensor-pits channels riddling  its skull, and for a moment one eye socket was eaten bare to echo Cassius' own scarred face.

Space Marine Legends: Cassius (ebook)