Why is Alkamos' Drop Rate So Low?

[malawiglenn]

Shar’Zul’s Worldeater has 2% chance to drop, how many runs do I have to do in order to get just one, assuming I am unlucky as fuck so the chances to drop fall down to 1%?

Not that I even need this weapon.

CL(at least one) = 100*(1-e^(-x/50))

and you want 99% CL, that is 230 runs (log_e(100) * 50)