The .300 WM is nothing to sneeze at. US Navy rifle match competitors have used it for decades for Wimbledon Cup shoots and other long range work, and the Germans chose to have their AW snipers rifles, designated Scharfschützengewehr 22, SSG22, equipped with a folding stock and Zeiss scope and chambered for the .300 WM cartridge.
Of course, you can do what I had to and begin with .416 Rigby cases....
To say nothing of that slick little .300 WinMag package the boys at Walther cobbled together...