min. 18 power to see the holes at 100 yds, also, you need to make sure your scope is parralax free, to at least 50 yards, or less.
anything else, is going to bounce your reticles all over at 100 yds, since most scopes don't zero out prllax to at least 100 or even 150 yds.
Your best bet of all would be a fixed power scope. like a weaver 24 or 36 x.