Which .300 ? What ammo are you using ?
For example, my .338 Win Mag with 250gr Partitions at 2700, is dead on at 200 yards, and is 1/8" low at 25 yards. Dead zero at 25 yards, moves my zero out to 225 yards. My .264 (when it gets here), should be about a 1/2" low at 25, and dead on at 200.
A .300 WSM/ .300 Win with a 180 Accubond moving 2950, will be -0.35" at 25 yards and dead on at 200.
So far, chrono numbers and ballistic programs have not failed me, but as he said, practice at the ranges you intend to shoot, and dont just make a guess out of it.