I don't see it listed anywhere.

It's a ranged attack, so normally this uses Agi plus weapon DR, which is represented by the number after St. Thus, 2+5 = 7, and always inflicting a critical in addition to other effects.

However, it is not a BS vs Defense attack, but a Resilience (To) vs Defense. With that in mind, I personally would think it's actually To + DR, thus 6+5=11 and always inflicting a critical.