300 Weatherby with 240s in match chamber with no freebore throat will stand up to any other caliber much less the RUM. My first HG was 300 Weatherby that has shot many 6" (10 shot) groups and is still going strong.
Brass is the cheapest part of a LR rig. For accuracy the knowledgable LR accuray buffs will tell you go with best bullets and brass first.
Buy some RWS brass and you can wear out a barrel with 40 pieces. Best brass costs a $1 each.
Key will be what weight will gun finish out at but Weatherby will go well out past 1000 accurately as anything.
If you are buying factory loads in either and shooting LR, you are going about it wrong and have problems even comparing that.
IF I wanted a really LR 30 cal it would be the 30/338 Lapua. Once again best brass and ballistics. However, that ain't no carry gun.
In my opinion, comparing cost of brass in a LR gun is like comparing custom made race tires to retreads for a NASCAR car. A custom LR gun will cost $1500-3500 so $100 for 100 pieces of the best brass is pittance.
Rem brass just is not worth the pain and effort to weigh and sort compared to quality brass.
BH