Short version-its to slow! Long version you can put RE25 in that case 2/3s the way up in the neck and compress it till it tries to push the bullet back and all you will have is a slow terd with excessive carbon build up from unburned powder, if you use a RE powder, RE19 is most suitable in that case for any bullet that should be used in it, 250-300grn pills are to much for that 338 case.