What is the parent case of the 264-win mag?
300 Win mag. It is the smallest of all the belted magnums that Winchester introduced.


What advantage/edge does the 264 have over the 6.5-06?
More velocity, about 200 fps with the same bullets.


Who chambers the 264-win mag?
I don't know of any "factory" rifles chambered for this cartridge any more. Although you could easily have a 300 win mag, 7mm rem mag, etc... rebarreled for it.


Does it look like anyone will chamber the 6.5-06?
Doubt it.