Imroved Critical

Prerequisite. Proficient with weapon, base attack bonus +8.

Choose one type of weapon.

Benefit. When using the weapon you selected, your critical range is doubled. (If your weapon critical hits on 20 (range of 1) then it becomes 19-20 (range of 2). 18-20 (range of 3) becomes 15 (range of 16)) 

Special. You can gain Improved Critical multiple times. The effects do not stack. Each time you take the feat, it applies to a new type of weapon.

This effect doesn’t stack with any other effect that expands the critical range of a weapon.