I would just about law odds that Phil Schoemaker's .458 mag. Alaskan guide rifle has a 22" bl. Too, he's shot moose at well over that 300yard range when the need arose. You'd be surprised what a good rifle shot can do with some practice and a .45 cal rifle.
A strong 350gr. at 2,450fps to 2,500fps, or a 400gr. at 2,350fps to 2,400fps will work just fine. It's just a lot more rifle than I need, these days for moose or big bear. When younger, I thought differently.