Rune Arm

Overview
Rune Arm (or Arm Cannon) is new kind of equipment implemented with Update 11 and the Artificer class. It goes into secondary weapon/off hand slot and requires Artificer Rune Arm Use feat (Artificer level 2 class feat) to use.

Rune Arms can be used in the offhand (with crossbow). The Rune arm has unique magical properties such as: adding magical weapon damage to the main hand, magical enhancements, and being craftable via Cannith Crafting system.

For the crafting purpose, the Craftable Rune Arm (+X) property written on a Rune Arm defines the maximum enchantment level it would permit. On a Rune Arm crafting shards are applied as if it was a trinket, and adding crafting enchantments raises the minimum level requirement accordingly (2 levels per 1 enchantment level of shard applied; the minimum level will equal (the total enchantment level *2) -1).

The Rune Arm also functions as a weapon as a free action (not restricting the users ability to cast or attack). The weapon uses Charges with five tiers, and these charges increase in damage the higher the tier (Rune Arms have a max tier level). Charges can be added standing still or while moving limited by the "Stable Charge Tier".

Rune Arms are currently only acquired by finishing certain quest chains, or in certain chests already known for dropping named and/or rare loot, such as the three dragon chests in Gianthold Tor; there are currently no randomly generated Rune Arms. The complete list of known Rune Arms, as well as their location, are below.

How it works
tapping it again fires it. You can keymap a different button if you wish.
 * Can be worn together with one-handed weapons and crossbows (not bows)
 * Tapping the Alt button will start charging it up,
 * You can Toggle the Rune Arm Use feat on while on an actionbar to make it keep autocharging.
 * Damage will be affected by Artificer level and charge tier.
 * Rune Arms will give a bonus elemental damage to the weapon in your main hand.
 * Blocking with a charge reduces the charge to it's maximum stable tier.


 * This doesn't seem to match the in-game DC, see this thread.

Increasing Rune Arm damage
10 + (Charge Tier + 1) + (INT modifier) + (Max Charge Tier - 1) + (Evocation Feat Bonuses)
 * Items and enhancements that increase spell damage or create spell criticals also affect rune arm damage.
 * Runearms don't benefit from items with a bonus to caster level on Evocation (Infused Chaosrobe, Might of the Abishai).
 * Runearms don't benefit from Prestige Bonuses to caster level (Radiant Servant will not boost Candlelight/Coronach/Tira's Splendor, for instance).
 * Runearms do benefit from the Spellsinger's Song of Arcane Might.
 * The DC of Rune Arm blasts is:
 * Items that increase Evocation DC do not seem to modify Rune Arm DC.
 * Different Rune Arms can be resisted with different saves (Fortitude/Reflex/Will).

List of named Rune Arms
As of Update 11 a total of 23 named Rune Arms have been added to almost all reward list across the game (Sharn Syndicate being the exception, which doesn't seem to award one) and to some other named loot/raid chest. Items are Bound to Account unless otherwise noted.

Max Charge Tier II:
 * Candlelight - Light Spirals: Lesser Undead Guard, Lesser False Life, Rune Arm Imbue: Light I, Craftable Rune Arm (+2) [ML:3, BTA] - Catacombs
 * Chulchannad's Claw - Cold Bolts: cold absorption - 10%, Inherent Cold Resistance -5, Rune Arm Imbue: Cold I, Craftable Rune Arm (+3) [ML:5, BTA] - Phiarlan Carnival
 * Flame Warden - Fire Blast: Lesser fire Resistance, Reflex Save +1, Rune Arm Imbue: Fire I, Craftable Rune Arm (+2) [ML:1, BTA] - The Lost Seekers
 * Flicker - Electrical Lash: Reflex Save +2, Power II, Rune Arm Imbue: Electrical I, Craftable Rune Arm (+2) [ML:3, BTA] - The Seal of Shan-To-Kor
 * Khyber's Fury - Exploding Fire Shot: Moderate Fortification, Rune Arm Imbue: Fire I, Craftable Rune Arm (+3) [ML:5, BTA] - Assault on Splinterskull
 * Thought Spike - Force Shot: Will Save +1, Rune Arm Imbue: Force I, Craftable Rune Arm (+2) [ML:1, BTC] - Redemption in Korthos Island

Max Charge Tier III:
 * The Disciplinator - Electrical Lash, Smiting Weapons,, Rune Arm Imbue: Electrical II Craftable Rune Arm [ML:9, BTC] (+4) - Plane of Night (raid chest)
 * Chimera's Breath - Electrical Blast: Proficiency: Bastard Sword, Diehard, Rune Arm Imbue: Electrical II, Craftable Rune Arm (+3) [ML:5, BTA] - Sentinels of Stormreach
 * Coronach - Coronach, Life Shield, Rune Arm Imbue: Light II, Craftable Rune Arm (+3) [ML:7, BTA] - Delera's Tomb
 * Hand of the Tombs Exploding Fire Shot: Disrupting Weapons, Inherent Fire Resistance - 5, Rune Arm Imbue: Fire II, Craftable Rune Arm (+4) [ML: 9, BTC on Equip]- The Chamber of Raiyum
 * Recoyle - Force Shot: Superior Impulse V, Anathema, Rune Arm Imbue: Force II, Craftable Rune Arm (+4) [ML:9, BTA] - Ruins of Threnal
 * The Devourer's Hunger - Superior Glaciation IV: False Life, Rune Arm Imbue: Cold 2, Craftable Rune Arm (+3) [ML:7, BTA] - Cult of the Six
 * The Pea Shooter - Acid Shot: Superior Potency III, Inherent Lesser Acid Resistance, Rune Arm Imbue: Acid II, Craftable Rune Arm (+3) [ML:7, BTA] - Into the Deep in The Red Fens
 * Trial by Fire - Fire Blast: Toughness, Inherent Fire Resistance, Rune Arm Imbue: Fire II, Craftable Rune Arm (+4) [ML:11, BTA] - Attack on Stormreach

Max Charge Tier IV:
 * Arcing Sky - Electrical Blast, Dodge Bonus +3, Inherent Electricity Resistance - 5, Rune Arm Imbue: Electrical III, Craftable Rune Arm (+5) [ML:13, BTA] - Gianthold Tor (Blue Dragon chest)
 * Chill of Winter - Freezing Ice Guard, Inherent Cold Resistance - 5, Rune Arm Imbue: Cold III, Craftable Rune Arm (+5) [ML:13, BTA] - Gianthold Tor (White Dragon chest)
 * The Turmoil Within - Attack Bonus +2, Inherent Acid Resistance - 5, Rune Arm Imbue: Acid III, Craftable Rune Arm (+5) [ML:13, BTA] - Gianthold Tor (Black Dragon chest)
 * Titan's Fist - Force Shot: Intelligence +6 (bugged and not working), Major Kinetic Lore, Rune Arm Imbue: Force III, Craftable Rune Arm (+4) [ML: 11, BTC] - The Titan Awakes (Raid chest)

Max Charge Tier V:
 * Animus - Exploding Fire Shot: Banishing Weapons, Taint of Evil, Rune Arm Imbue: Fire IV, Craftable Rune Arm (+5) [ML: 19] - Devil Assault on all difficulties
 * Glorious Obscenity - Acid Shot: Enhanced Spot +5, Seeker +6, Mind Turbulence, Taint of Chaos, Rune Arm Imbue: Acid IV, Craftable Rune Arm (+5) [ML: 17] - Reign of Madness
 * Lucid Dreams - Force Shot: Nightmare Guard, Superior Potency VI, Arcane Lore, Mind Drain, Will Save -2, Rune Arm Imbue: Force IV, Craftable Rune Arm (+5) [ML: 19, BTA] - The Mindsunder (Disc-locked end chest)
 * Tira's Splendor - Light Spirals: Healing Amplification - 20%, Deathblock, Tira's Splendor, Embodiment of Law, Rune Arm Imbue: Light IV, Craftable Rune Arm (+5) [ML: 15, BTA] - Garamol (rare encounter in The Subterrane)
 * Toven's Hammer - Electrical Storm: Lightning Strike Weapons, Superior Potency VI, Exceptional Fortification (10%), Missing Parts, Rune Arm Imbue: Electrical IV, Craftable Rune Arm (+5) [ML: 19, BTC] - The Master Artificer (Raid chest)