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).

Table of named Rune Arms
As of Update 11, a total of 23 named Rune Arms have been added to the game. They most commonly appear in the end-reward lists in most chains or quests (Sharn Syndicate being the exception, which doesn't seem to award one). They may also be found in some other named loot/raid chests.