Improved Critical

Type: General, Fighter
Source: Player's Handbook

Choose one type of weapon, such as longsword or greataxe. With that weapon, you know how to hit where it hurts.
Prerequisite: Proficient with weapon, base attack bonus +8
Benefit: When using the weapon you selected, your threat range is doubled. For example, a longsword usually threatens a critical on a 19-20 (two numbers). If a character using a longsword has Improved Critical (longsword), the threat range becomes 17-20 (four numbers).
Special: You can gain this feat multiple times. The effects do not stack. Each time you take the feat, it applies to a new weapon.
The effect does not stack with any other effect that expands the threat range of a weapon (such as the keen edge spell).