Luck favors the best prepared
The point is that the WSM case is quite capable of some impressive accuracy, only been out for 12 years and already holds some serious credentials in long ranged matches and now a world record, don't own any 300 magnums so I cannot vouch for it from personal experience, just what I have read. Engineers at Browning have said the 270 WSM is in general the most accurate cartridge they have ever dealt with, I own one and have found it quite easy to develop accurate loads, 130gr SGKs and 61.5gr of IMR4350 shoots one tiny hole in my Savage at 100, very impressed.