it doesn't matter what you go with. 7x57, 7mm-08, 7mm rem mag or even 7mm weatherby mag. no matter what you get it will kill any deer in the world within 400 yards and any farther you will need an incredible amount of skill, a very expensive setup and very firm position to shoot from. your cartridge length would be the least of your worries in that position.
ignore my complete lack of capitalization. I still have no problem correcting your grammar.
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