Talk:Corki/Strategy/@comment-24363589-20140929073030

The real reason to always get The Black Cleaver instead of Last Whisper on corki is not because of how fast he can stack it (although that is a very nice perk), rather it is because the percentage armor shred applies BEFORE his E armor shred, allowing them to stack fully. In contrast, Last Whisper's armor pen applies after the target's armor has been reduced by E. The result is that assuming you've maxed E, which you should have if you are getting an armor pen item, the opponent needs to have 170 armor for LW to be more effective even if you only land have of E's armor shred. That number skyrockets to 240 armor if you land all the stacks for 40+25% armor reduction.

MATHS:

X => target's armor

0.65 (X - 20) = effective armor with LW and half stacks on E

0.75X - 20 - 10 = effective armor with BC and half stacks on E

0.65 (X - 20) = 0.75X - 30

0.65X - 13 = 0.75X - 30

30 - 13 = 0.75X - 0.65X

17 = 0.1X

X = 170

0.65(X - 40) = effective armor with LW and full stacks on E

0.75X - 40 -10 = effective armor with BC and full stacks on E

0.65(X - 40) = 0.75X - 50

0.65X - 26 = 0.75X - 50

50 - 26 = 0.75X - 0.65X

24 = 0.1X

240 = X