It depend on which Pokemon is using it, and what it's level is.
Say if you're Pokemon is Dewgong at 70 lvl, it's a clean kill, but if it's 64 lvl instead, it barely misses taking it out at 252 sp.atk investment.
EDIT: If you're Pokemon is a Walrein at lvl 52, and if you have 0 investment in special attack, it would do just above half to a lvl 70 Rayquaza. However this also means two hits is a sure knock out.
Hope I helped!