SRD:Lightning Blast (Epic Weapon Enhancement)
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On command, a lightning blast weapon crackles with electrical energy (though this deals no damage to the wielder). On any hit, lightning coruscates around the creature struck, dealing +3d6 points of bonus electrical damage. On a successful critical hit it instead deals +6d6 points of electrical damage (or +9d6 if the critical multiplier is x3, or +12d6 if the critical multiplier is x4). Bows, crossbows, and slings with this special ability bestow the bonus electrical damage upon their ammunition.