When you mount a scope 1.5 inches above the bore, most center fire rifles (except the .30-30, .45-70, pistol cartridges) will place their bullets across the line of sight first between 23 and 27 yards, depending on velocity...this normally gives you a zero at around 200 yards, and puts you 1-2 inches high at 100 yards...and about 3-6 inches low at 250 yards...

When sighting in, I always start at 25 yards point of aim, then back to 100 yards and adjust for +1.825 inches with my 7mm RM, then out to 250 yards, and adjust for zero. This gives you a very precise rifle with a minimum use of ammo.

Another popular method lately is to zero the rifle at 200 yards with a BDC type reticle and use a laser range finder...WARNING...the BDC is terrific but not necessarily precise...the 300 yard dot may be 250-350...you really need to shoot enough to verify the distance for each...and write it down somewhere handy...