Arc Weaponry
LIGHTNING GUNS WOOOOH! Arc Weapons are a type of weapon utilised by the armed forces of the Adeptus Mechanicus. Unlike the other 'lightning gun' used by the Thallax, Arc Weapons are actually tried and true lightning weaponry. They are powered by bulky perma-capacitors shipped from Mars' great repositorum; some of these zinc-plated blocks store energy from days when the Imperium was young. Arc Weapons discharge energy with a loud crack, firing blots of blue-white electricity that can fry a man's brain or overload a war machine's data-cortex in a second.
On the tabletop they are basically Imperial Haywire weapons; come in pistol or rapid fire format for your pleasure. Also has a nice S6 if you don't want to shoot at vehicles for some reason, though at only AP -1 you'll need some luck to do more than scratch a Rhino’s paint.
For the more lethal and overpowered Necron variety, see here:
Variants
There are a few variants of the Arc Weapons.
Arc Maul
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Shooting from afar is fine and all, but in the grim darkness of the future, any tech that can't be applied at close range will be looked at with shame. Thus, the arc maul combines the power of a bludgeon weapon with the energy and electricity created by an arch engine to make one brutal CQC monster.
Arc Pistol
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A small pistol based on Arc technology and most commonly used by Skitarii Vanguard/Ranger Alphas. Trying to use this to 'charge up' your phone or any other electrical appliances is heavily frowned upon by the Adeptus Mechanicus and the Priesthood of Mars.
Crunch wise, it is a very nasty little weapon. Essentially it is a 12" S6 AP -1 Pistol that can shred infantry (it wounds guardsmen on 2s) and can annoy vehicles as well. It works really well when paired with its much bigger brother, the Arc Rifle due to the Arc Rifle's rapid fire rule.
Arc Rifle
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A rapid firing Arc Weapon used as a special weapon in Skitarii Vanguard and Ranger squads. The Arc Pistol's bigger brother. This is the gun you need when you want a little bit more range in your lightning cannon. Basically your typical tesla gun in sci-fi....no not THOSE Tesla weapons..
Crunch wise on the tabletop, it is known to possibly be one of the best-looking guns the Skitarii have. It's 24" Rapid Fire, which means it pairs well with its little brother.
The Arc Rifle is one of the most common Arc weapons found in the Mechanicum.
Vultarax Arc Blaster
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The Vultarax Arc Blaster was a type of Arc Weapon. Primarily mounted on the Vultarax Class Robot, it was a a versatile weapon capable of burning out the cogitators and engines of enemy vehicles and robots.
The Vultarax Arc Blaster is the only airborne adapted Arc weapon designed during the later years of the Great Crusade. During the Horus Heresy, the Arc Blaster found its use against both traitor and loyalist AdMech forces during the civil war on Mars.
The large cybernetic machinery within the Mechanicum made its extremely vulnerable to Arc weapons with the Arc Blaster being one of the more notorious examples used during the civil war, with the Arc Blaster permanently shutting down vast swaths of battle automata and combat servitors in one shot.
Heavy Arc Rifle
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A heavy Arc Weapon designed to slay the Daemon machines of the Dark Mechanicum, Heavy Arc Rifles send out shallow parabolas of crackling energy that revolve around each other, forming triple helixes as they blast forth. Should these ground upon a metallic target, they will swiftly overload its circuits and banish its animating spirit to the ether. Heavy Arc Rifles are part of the standard armament of Cult Mechanicus' Kataphron Breachers.
In terms of Crunch, it's a 36" 2 shot S6 gun. Comes default on Breachers. Use it to pop open any vehicles giving you grief or to reveal the tasty transported center.