Mistake #3: Assuming what you read is true
Not everyone lives where they can shoot at 400-yard targets. So they consult the ballistic charts to find a suitable remnant beyond 200. A logical choice. But if the mainstream news reports haven’t disabused you of confidence yet, the charts should. For as long as mice have had tails, factory-loaded 180-grain bullets have come out of .30-06 rifles at 2700 fps. My Oehler, however, has clocked them from just under 2600 to 2835 fps (standard loads, not super-duper, 22″ barrels). The difference in a 400 yard drop is almost 5″, given the same bullet shape. If the faster charge sends out a sleeker bullet, the disparity may be much greater. A round nose bullet at 2600 fps plummets 38″; a boat tail Spitzer at 2,800 drops 23″.
Another increasingly common variable is the height of your sight above the bore line. Back when 2-1/2x Lyman Alaskans sat so low on Tilden mounts they nearly kissed the receiver, line of sight was held close to the bullet’s course until gravity dissolved the bond. Soup can target bells and Picatinny rails now raise sight lines, increasing their angle relative to the line of sight. For any given first crossover, the zero range then moves further away.
To confirm a zero, you need to shoot groups on paper at the indicated distance with the load that you will use on the hunt. Same for seeing where the bullet lands beyond zero range.