Gravis plasma cannon

"With a Weapon that has a Breaching (X) Special Rule there is a chance that a Wound Test may result in the Wound ignoring Armour Saves."
When any Wound Test is made for an attack with the Breaching (X) Special Rule, if the result of the Dice roll, before any modifiers are applied, is equal to or greater than the value of X attached to this variant of the Breaching (X) Special Rule, then if a wound is inflicted by that Wound Test, that wound becomes a 'Breaching Wound'.

A Breaching Wound is always treated as having an AP of 2 regardless of the Characteristics of the Weapon used to make the attack.

"With a Weapon that has a Breaching (X) Special Rule there is a chance that a Wound Test may result in the Wound ignoring Armour Saves."
When any Wound Test is made for an attack with the Breaching (X) Special Rule, if the result of the Dice roll, before any modifiers are applied, is equal to or greater than the value of X attached to this variant of the Breaching (X) Special Rule, then if a wound is inflicted by that Wound Test, that wound becomes a 'Breaching Wound'.

A Breaching Wound is always treated as having an AP of 2 regardless of the Characteristics of the Weapon used to make the attack.

"Weapons with this Special Rule may inflict Hits on the Models making Shooting Attacks with them."
When the Controlling Player declares that attacks will be made for a Model using a Weapon or Profile that has the Overload (X) Special Rule, any Hit Tests made for those attacks that result in a number that is equal to or less than the value of X attached to the variant of the Overload Special Rule that the Weapon had, before any modifiers are applied to the roll, are Misfires.

For Weapons that do not make Hit Tests, such as Weapons with the Template Special Rule, instead roll a number of Dice equal to the Firepower Characteristic of the Weapon used to make the attack after the attack has been declared and the number of Models hit is determined. Each Dice that results in a number equal to or less than the value of X attached to the variant of the Overload Special Rule that the Weapon had creates a Misfire. This does not affect the number of Hits on the Target Unit created by this attack.

For each Misfire, the Unit for which the Hit Tests were made suffer a Hit - these Hits must form a new Fire Group or Strike Group, referred to as the 'Misfire Group'.

Once the current Shooting Attack and any Reactions triggered by it have been fully resolved, the Misfire Group must be resolved. A Misfire Group is resolved in the same way as any other Fire Group or Strike Group, using the Profile of the Weapon used for the Fire Group or Strike Group it was created from. Wounds, Glancing Hits, or Penetrating Hits from this Misfire Group are allocated by the Controlling Player, and must be allocated toa Model that made attacks as part of the Fire Group or Strike Group that generated the Misfire Group. If a Hit from a Misfire Group is generated by an attack made by a Model with the Vehicle Type, then it is resolved against the lowest Armour Value from all of the Model's facings.

Hits, Wounds, or Casualties inflicted upon a Unit as a result of this Special Rule do not cause Leadership or Cool Checks, and Hits inflicted as part of a Misfire Group do not trigger any Special Rules that take effect as a result of a certain value on a Hit Test.

"Attacks made with the Blast (X) Special Rule use a Blast Marker to determine how many Hits are caused."
When making attacks with a Weapon that has the Blast (X) Special Rule, before any Hit Tests are made, a Blast Marker must first be placed to determine how many Hits may be inflicted by the attack. The Player making the attack must place the Blast Marker indicated in brackets as part of the Special Rule so that the hole in the middle is entirely over the base of any one model in the Target Unit. Once the blast Marker has been placed, the Player making the attack must make a Hit Test for the attack, and each Model from the Target Unit that is fully or partially under the Blast Marker will suffer 1 Hit if the Hit Test is successful.

*Hits on Other Units*
If any Models form Units other than the Target Unit are fully or partially covered by the Blast Marker, then a new Fire Group must be created for those Hits and set to one side. Continue resolving the Shooting Attack on the original Target Unit, and once that Shooting Attack has been completely resolved begin a new Shooting Attack to resolve those additional Fire Groups generated for Units other than the original Target Unit.

If the Hit Test is unsuccessful then no Hits are inflicted and the Player making the attack must make a Scatter Roll for the Blast Marker (see the Rules for Scatter in the Warhammer: The Horus Heresy - Age of Darkness Rulebook). Once a Scatter Roll has been made for the Blast Marker and it has been moved, one Hit is inflicted on a Unit for each Model from that Unit that is wholly or partially covered by the Blast Marker.

"Weapons with the Heavy (X) Special Rule gain +1 to a Characteristic when Stationary."
When making a Shooting Attack with a Weapon that has the Heavy (X) Special Rule, a modifier of +1 is added to a Characteristic if the Model with that Weapon is part of a Unit that remained Stationary in the Controlling Player’s previous Movement Phase. If the Characteristic listed is AP, then instead it improves the AP by one Step. The value of X in the specific variant of the Heavy (X) Special Rule determines which Characteristic gains the +1 modifier.