I have seen pictures from Alaska of folks shooting Bear with 50 BMG's.

http://www.barrettrifles.com/pdf/Manual-95.pdf

Rumor has it this cartridge is illegal in Africa because of its military roots--- I dunno, but am sure someone will!

Is the big 50 a legit hunting rifle?
Analyze your feelings--
Is it precise enough? Yes
Is it portable? Yes
Can it be had in a bolt magazine gun? Yes
Can it be loaded with "hunting bullets? Yes

Or does it foul out for other reasons?
Is it too heavy for one man to carry long distances(like a 600 Nitro,700 nitro, or 4 or 8 bore would be)?
The cartridge is not "sporting"?
It can't be used to hunt, only shoot!!

All this said, a friend has a 50 and I really like shooting it out to 500 yds, I think 50's are a blast!!