Servus Elk686! Es ist schon lange her, seitdem ich in Oesterreich war. Herzliches Wilkomen.
OK Gents, Elk686 is from Austria where there is very little public land available. So I'm guessing there will not be much opportunity to stretch the legs of his 338 Lapua, unless he lives close to a shooting range catering to long range shooters. So bullet BC isn't going to be as big a concern for him as it is for us. The largest game animal in Austria would be the Hirsch, or red stag - something close to our elk. I believe most all hunting opportunities will be found on private game preserves.
Like scrmblr suggested: I would go with a 250 grain bullet that is easy to buy in your area. With the extreme power of a 338 Lapua, you don't have to focus on loading premium bullets in order to get great terminal performance. Barnes is an excellent choice, but if they are hard to find, then try the Nosler Accubond or even some of the Hornady SST. Over here, the Berger and Sierra offerings seem to be popular in the 338 Lapua.
Nosler's reloading book suggests a starting load of 90.0 gr. of H-1000 for the 338 Lapua with a 250 gr. bullet and a max load of 94.0 gr. The most accurate load in their test rifle was with 94.0 gr. Like most big magnums, they seem to perform best when their cases are full. Viel Gluck!