My Winchester model 70 .300 win mag is the same way. Long throated. It's not uncommon in magnums. Just load to a COAL about .010" to .015" less than max magazine length. If it's not shooting well then different powders and bullet weights are the way to find accuracy.
The one big thing to remember is it doesn't have to be loaded to however much off the lands for a load to be accurate. Weatherbys are long throated and can be extremely accurate. Same goes for other long throated magnums.
Don't get caught up in worrying about distance to the lands.
