Volkite Weaponry
Volkite Weaponry is an ancient and advanced class of weapon based around imparting so much heat on the enemy that he literally bursts into flames inside his armour (think Martian Heat-ray, literally Martian actually, since they're the ones who make the good-shit like Volkite weapons), these flaming victims then cause more damage to their squad as they run around their buddies emitting the temperature of a small furnace. It's only real drawback is it's relatively short-range compared with more conventional weapons (though not quite as bad as Melta weapons). Way back in pre-heresy days when the Great Crusade was just starting out, there were enough of these rape-machines to equip every single Space Marine Legionnaire with one. Unfortunately as the crusade grew demand far outstripped supply, resulting in it's relegation to special weapon. Like most cool Imperial weapons, the technological know how to make Volkite weapons was lost as a result of the Horus Heresy.
Volkite Weapons
Volkite Serpenta
The pistol of the family, highly effective and powerful sidearm but with obviously low range and rate of fire, and the favoured ranged weapon of a certain Sick Fuck. The Adeptus Mechanicus still have a few of these on hand, but like most of the good stuff, instead of taking it apart and reverse engineering it, they instead keep them locked in stasis vaults and ogle them.
Volkite Charger
The rifle of the family, as stated previous, at the outbreak of the Great Crusade these things were the goddamn standard weapon for the Adeptus Astartes, which I'm sure was a terrifying prospect for the enemies of the Imperium. Unfortunately their laborious construction resulted in them being relegated in favour of the Bolter, which was much easier to manufacture and supply, which was important as the crusade grew from a few thousand marines, a planet, and a moon to many hundred thousands of marines, quadrillions of Imperial Army troops and an entire galaxy of shit to conquer.
Volkite Caliver
Somewhat comparable to a light squad support weapon, longer and bulkier than the Charger, though still loaded from a box magazine and fairly easy to carry. With a better range and rate of fire than the Charger at a cost of being unable to fire on the move.
Volkite Culverin
The heavy weapon, bulky, powerful, with a massive rate of fire and equally large ammunition requirement. It's like a Heavy Bolter if it fired even faster and it's shots caused the enemy to spontaneously combust.
Volkite Carronade
The big one. Disgusted by the prospect of the largest weapon in a given type being able to be held by a person, those crazy Martians decided to supersize it and put it on the turret of the Fellblade super-heavy tank. At first glance it's almost comically short-ranged for a Super-Heavy tank weapon, but when you consider it hits absolutely everything in a straight line (which is as wide as the weapons barrel, which is about the same as the height of a Space Marine) between it's smoking barrel and it's max range, turning entire tank columns into craters and reducing infantry formations into screaming, flaming soon-to-be-corpses who proceed to set their own allies alight, it ends up looking pretty good. That said, it hits YOUR units too, so don't place anyone you don't want to lose in front of it when it fires.