Is there any overarching reason to maintain caliber compatibility with his Father-in-Law? Is that the only person he hunts with? Will he do all his reloading for him? Otherwise as a grown man he should be able to accept any of the standard deer calibers. I think 7mm-08 is about as perfect as it can get, but if he ever plans on hunting other game besides Eastern whitetail then that should be a consideration. How about .270 Winchester? .280 Remington? .30-06? Certainly .308 Winchester.
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