I watched an episode on TV where they were shooting a .375 Cheytac from Snowy Mountain Rifles for Elk. Impressive. I've always wanted one since, but, don't live far enough away from anything.
There's several manufacturer that makes action for big cartridge like the Cheytac. Fotis and I use Stiller TAC 408. JJRock, BAT, Barnard, Pierce to name a few.