I have had a couple, never chronied my current one. I have a bad head for numbers but with 250+ grain bullets I did not seem to lose much. I generally use h4831, sometimes varget for lighter 200 and 225 deer loads but I never cared about the velocity on those much tbh
338 wm often gets handicapped by being put in big heavy guns when the real advantage is that it can be put in smaller lighter guns than full on stopping rounds and still be manageable for range use and follow up shots.
If you go into with the attitude that it is a “ big 30-06” shooting 250s at a similar trajectory to ‘06 180s you will not be disappointed. A lot of guys seem to hear 338 and think “ whizz bang magnum” not “ med bore potato chucker”, their loss
I think a 338 in a good stock with a carbine length barrel is the perfect rifle for hunting north and central BC, boreal to rainforest. Even if you aren’t changing loads up there is no tag you could buy or draw that couldn’t be filled with 250 grain 338 wm loads
Ymmv as always