Improved Critical feat

[Heather 540]

When you take the Improved Critical feat, it says: When using the weapon you selected, your threat range is doubled.
What does that mean?

[Scrapper]

if a weapon has a threat range of 19-20 x2, effectively a 10% chance of a critical hit, Improved Critical(Weapon Name) will have that range doubled, in this case now 20% or 17-20 x2.
for lower crit weapons like a Great Axe with a threat only on a 20 (x3)[5%] it would now crit on a 19-20(x3)[10%].
for a higher crit like a Scimitar, 18-20 (x2)[15%] it becomes 15-20 (x2)[30%].
Improved Critical only works with the weapon it was selected for, but may be picked up more than once for additional weapons.

[Gisher]

Let's say that you like using a Rapier. Normally it has a Threat Range of 18-20. So if you make an attack roll and get a natural 18, 19, or 20 (and hit) then you threaten a Critical Hit. If you have Improved Critical (Rapier) then that Threat Range is doubled. So you would threaten a Critical Hit when you succeed in hitting on a natural 15, 16, 17, 18, 19, or 20.

[2bz2p]

If you normally threaten on a roll of a natural 20, you now threaten on a roll of a natural 19 or 20 (so long at the 19 still hits).

If the weapon threatens on a natural roll of 19 or 20 (like a dagger), you now threaten on a natural roll of 17, 18, 19 or 20 - as long as the 17, 18 and 19 actually hit.

You cannot stack two sources that improve a threat range (Keen weapon with Improved Critical feat has no improved effect, but does allow the keen weapon to still have improved threaten in an anti-magic zone because the feat is Extraordinary and not SU or SP)

Hope that helps.

[Scrapper]

Improved Critical functions the same as the Spell: Keen Edge and the Magical Property Keen, but does not stack, however, spells and properties can be dispelled or rendered inert in anti-magic fields while the feat remains viable.

[Heather 540]

Ok, I think I get it. The Critical Hit range is what gets doubled.

I'm making a Whirling Dervish Swashbuckler and get the effect of Improved Critical for all one-handed or light piercing melee weapons and scimitars for free at level 5.