Understand that the larger the caliber of the bullet, the MUCH larger the bullets need to be in order to be ballistically efficient. I think you will have a bit more than the bullet to limit your long range accuracy. It all boils down to how accurate the rifle ends up being. Big does not mean accurate, in fact often it is the exact opposite. A 338WM is a good large game, medium distance hunting cartridge, but if it isn't accurate, you can do as much non-lethal wounding/maiming with a 338 as you can with any other cartridge.
Bottom line is you will have to work on a good, accurate short distance load and how tight you can get that will dictate accurate you can expect the long range group to be, but you must add in what shooting aids you will have at the time.
Remember that a 1.5" group at 100 yards is 3" at 200, 4.5" at 300, 6" at 400 etc. under ideal conditions.
Long range shooting is a challenge. Accurate Long range shooting takes a good shooter, a good firearm and a good, tuned ammunition. The results will be governed by the weakest of these three.