The Psycannon is a weapon created specifically by the Imperium to combat daemons and the other entities of the Immaterium. The bolt is devastating to the psyches and physical bodies of psychic creatures, such as psykers, daemons, and daemonhosts, those individuals who have been possessed by the daemonic entities of the Warp. The Psycannon is a more powerful version of the Bolter, equivalent to a Heavy Bolter, utilising high-caliber, psychically-charged, ritually-inscribed silver-tipped bolts. The negative psychic charge and anti-daemonic ritual inscription on every Psycannon bolt allows them to pass through any defensive shielding, whether it is created by psychic energies or generated by gravitic technologies such as Void Shields or Conversion Fields. The weapon has an anti-gravitic suspensor incorporated into its mechanism to offset the weight and this allows it to be fired on the move although at the cost of a reduced effective range.
The Psycannon is a weapon exclusively used by the agents of the Ordo Malleus of the Inquisition and its Chamber Militant, the Grey Knights Chapter of Space Marines. There are a few notable exceptions to this general rule, such as the Inquisitor Gideon Ravenor of the Ordo Xenos, whose armoured grav chair was fitted with a pair of such weapons. The Psycannon is generally wielded with both hands by the Grey Knights who are assisted in making use of it through the efforts of their Power Armour. It is used with two hands by most other operators as well, although members of the Grey Knights' Terminator Squads mount the Psycannons on their arm instead. The method of feeding ammunition is similar to that of the Heavy Bolter used by the Space Marines, which uses an ammunition belt running from the ammunition store located within the operators' armoured backpack.
The Psycannon can also be used in conjunction with a device called a Mind Impulse Unit. The Psycannon is linked to the mind of the user and is fired by his or her mental volition. This has the advantage of allowing the user to fire the weapon while keeping both hands free, and allowing the user a greater intimacy with his weapon's internal workings, such as its current amount of remaining ammunition or its barrel temperature. Also, if the user is a psyker, they can infuse their own power into the weapon, adding to its already devastating effect. This is a common technique used by the Grey Knights, the only Astartes Chapter comprised entirely of psykers.
High-ranking members of the Ordo Malleus may use Bolt Pistols and standard Bolters which fire down-sized versions of the Psycannon's ammuntion. These Psycannon bolt rounds are less effective than the standard Psycannon's bolts, but more powerful than the same-sized bolts of a non-psychically charged weapon.
- Codex: Daemonhunters (3rd Edition)
- Codex: Grey Knights (5th Edition)
- Realms of Chaos: Slaves to Darkness (1st Edition)