I agree with Fosgate5 on the 338 Lapua (tactical/sniper rifle) think it's got the one of biggest bolt face @ .558. 338-378 Wby is only .579,300RUM is
.534.
The 300RUM was made more as a hunting rifle and what appeals to some "doesn't have the belt" so it headspace like a standard caliber. I took a pretty nice bull couple years ago with a factory 300RUM good elk rifle IMHO. My gunsmith has build afew 338 Edge off the 300RUM case for some elk hunters and we have afew in our gun club that shoot the Rem 700 in 300RUM for elk hunting. There is plus/minus with every caliber depending who's posting. here something on the 338 Edge
http://www.longrangehunting.com/articles/338-edge-1.php