These bulky automatic weapons differed from the more common Heavy Bolter only in calibre, as the Mauler Bolt Cannon uses substantially larger bolts than its counterpart and thus has a proportionally larger and more robust frame to handle the increase in recoil.
The Mauler Bolt Cannon was intended to provide heavy support to Mechanicus units in the field. It had originally been developed for use by the Skitarii Legions, but found its true home among the Battle-Automata of the Legio Cybernetica. The design of the weapon was a jealously-guarded secret of the Mechanicus.
Ardex-Defensor Mauler Bolt Cannon
The Ardex-Defensor Pattern of the Mauler Bolt Cannon was a massive, Titan-grade variant of the standard Mauler Bolt Cannon that was employed as a secondary armament on the Warbringer Nemesis-class Titan. Its massive bolts were capable of easily penetrating armoured vehicles and other large combat walkers.
- The Horus Heresy Book Two - Massacre (Forge World Series) by Alan Bligh, pg. 267