ORIGINAL: kelbro
Depends on the scope height above the centerline of the bore, velocity, and a few other factors. There's no substitute for sighting in at the ranges that you anticipate taking your shots at.
exactly. 27 is the right number for an exact cartridge, with an exact scope height, and an exact barrel length. alter any of those and 27 may not be the number anymore. if you insist on sighting in this way, find a ballistics program and check the exact set up that will be used. this can be a good way to sight in, but you need to do your homework on the exact set up you'll use first.