Two Dreadnought Fists w/ Built In Dreadfire Heavy Flamers

If a shooting weapon has the twin-linked special rule, or is described in a model's wargear entry as twin-linked, it re-rolls all failed To Hit rolls.

For a Blast weapon, if the scatter dice does not roll a hit, you can choose to re-roll the dice with a Twin-linked Blast weapon. If you choose to do so, you must re-roll both the 2D6 and the scatter dice. 

Twin-linked Template weapons are fired just like a single weapon, but must re-roll failed To Wound rolls and armour penetration rolls.

Ranged weapons with this special rule roll an additional D6 when rolling to penetrate a vehicle's armour at half range or less. If the weapon is more than half its maximum range away, it rolls to penetrate as normal.

If a weapon has both the Melta and Blast special rules, measure the distance to the centre of the blast marker after it has scattered. If this is half the weapon's range or less, all hits caused by the blast marker roll an addition D6 when rolling to penetrate a vehicle's armour. If the centre of the blast marker is more than half the weapon's maximum range away after scatter, roll to penetrate as normal.