But for 300 and 600yd the 7mm-08, 6mmCM, .243, and even .308 are also good choices (yes, there is some premium match available for 7mm-08). Heck, even a lowly .223 can do ok at 600 with the factory 77gn loads.

If not reloading it all depends on what you can find on the shelf....and then order a ton of it :)