You need to know that your rifle is firing where you expect it to. If you are confident in the integrity of your weapon then you will not be second-guessing what went wrong. If you miss an easy shot you'll know it was the shooter. You need to know the exterior ballistics of your gun for the load you are shooting if you expect to shoot deer at long distances. "Long distance is a function of many things, e.g., is it windy, is the deer moving, are you breathing heavily, factory loads (not precise) or home loads (can be extremely precise). The longest shot I had was with the rifle that made the pattern at left, my 1976 Weatherby .270 magnum. It was 475 yards under ideal conditions. The longest I ever saw was a shot my dad made, just over 600 yards, on the run, solid chest shot, with one shot.

 

    I have my ballistics memorized out to 500 yards. My .270 Weatherby Magnum is sighted-in at 2.4 inches high at 100 yards. At 175 yards the bullet is 3.5 inches high and at 350 yards the bullet 3.5 inches low. This means that with a defined kill zone of 7 inches - from 0 to 350 yards - all I have to do is aim the gun at the vital zone, and squeeze the trigger. Now that my Weatherby is broken-in, the baliistics have actually improved over this factory test firing.