One of the best things about any AR is you can easily change calibers by swapping out the entire upper receiver assembly, and most manufacturers sell them separately. There is a ton of info over @ AR15.com. Good luck.
Just buy a complete upper in 6.8, then you can switch back and forth at will. Keep in mind that with the infection of BRD*, that it wouldn't be too long before you got a separate lower so you would end up with 2 complete rifles!
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