That depends on the consistancy of the rifle and just as importantly, your ability to shoot the rifle and put the bullet on the mark at long range.
While the 338 Lapua has plenty of energy for taking big game out to even a mile or more, the first topic to discuss is being able to put that bullet in the correct location to cleanly harvest the animal targeted.
Simply put you have enough performance in that round to reach well past a mile but that is not what will determine how far you can get a one shot kill at. Greatly depends on you and the rifle.
Good Shooting!!
Kirby Allen(50)