Dwarf Bolt Thrower

Bolt Throwers are simply larger versions of the crossbow, able to fire heavier bolts over greater distances. Engineers still vie with each other to invent Bolt Throwers with greater range, loading speed or accuracy. Practical to a fault, the Dwarfs place more trust in an old, proven Bolt Thrower that has fired reliably for generations. The Bolt Thrower remains an important part of the Dwarf arsenal because it can be built and maintained cheaply and is accurate enough to bring down monsters such as Wyverns or Trolls with a well-judged shot. Its direct trajectory of fire and uncomplicated mechanism also enable it to be used effectively underground, and without obscuring everything around it in choking smoke.

Source

 * Armybook: Dwarfs (7th Edition) pg. 44