When making a cannon, with each hammer blow an Engineer strikes, a Runesmith must recite a special litany. This can take weeks to complete.
Source: Warhammer Armies Project: Unofficial 9th Edition (v2.2)
Rune of ForgingURL Copied!
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Unique25 points
Cannon only. A war machine engraved with a Rune of Forging can re-roll the artillery dice whenever a misfire result is rolled; however, you must accept the result of the second roll. Multiples of this rune have no further effect.