The RUM is a .30 cal speciality cartridge. Great for guys who can handle the recoil and muzzle blast and who regularly shoot big game at 400+ yards.
In reality though, even a "regular" 300 win mag is more than most hunters need, or can handle.
Heck, even a 30-06, with proper loads, will put down your deer, bear, moose, at ranges far longer than 90% of hunters can shoot effectively.
There's nothing wrong with the RUM, but too many guys buy them because of all the impressive numbers the RUM posts, and then end up selling them due to them being simply too much in every department, from ammo cost, to recoil, to muzzle blast.