Greater Critical (3.5e Feat)
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 Greater Critical [General]
This effect doesn’t stack with any other effect that increases the critical multiplier of a weapon. If an effect extends a weapon's threat range (such as the Improved Critical feat or the keen weapon special ability) the increased critical only applies to the weapon's base threat range. The extended threat range uses the weapon's base multiplier.A fighter may select Greater Critical as one of his fighter bonus feats.
Dungeons and Dragons -> Feats -> General.