I have a 300 Win Mag that I load 200 gr accubonds or partitions in and use on about everything I hunt. I've used 150 and 165 gr bullets of traditional construction and didn't like them, for the simple fact that I usually ended up with a bunch of bloodshot meat on most all animals mentioned, shot at fairly close ranges. I've taken moose, elk, deer, caribou, muskox antelope and bear with the 200 grainers and am much more satisfied with the 200's than the lighter ones. Poleaxed some moose at a bit beyond 300 yds with the 200's, so they shoot flat enough.
Of course the bloodshot issue may not be as big of an issue if the shots were out beyond 200yds or so.
The important thing is for your son to shoot the rifle sufficiently enough to become comfortable and confident with it, and to ensure lethal shots out to the ranges he could possibly be shooting at, no matter what bullet weight is chosen.
