The Horus Heresy novella The Serpent Beneath
A single genestealer bounds at you from out of the shadows. It is a horrid xenos breed that is deserving of the your storm bolter's vengeance. You put it down with an economical blast from your weapon before moving on through the space hulk. Return to the MAP to continue your journey, remembering to subtract 1 blast from your original total of 12. If you had no ammunition left at the beginning of this encounter then you already know that you are dead. Return to the Map and try again.