Its been done. I started one 4 years ago but never finished it and built a 308 instead on the reciver. I still have a remington stainless 6.8 barrel for a build. the grendal is a better way to go if you want to keep the AR length mag well but why your not resricted to it like a AR?? better IMOO to jus t build a 260 remington or 7mm-08 or 243 and load a little light. There is a 6.8spc II now with a slower twist that allows hotter loads so it will almost do what Remington lied about before they virtualy abandoned the round. If your going to hand load jusgt build a 7mm-08 or 260 ammo would be cheaper if formed from 7.62x51 brass and it would blow he doors off the AR intended 6.8 spc.
It a good round but ammo is pricey. I still have the barrel and you see them on gun Broker from time to time. or simply rechamber a 270 barrel. You see Take offs on GB all the time for around $35 or so all the time. I say go for it. a ar mag addapter and a AK 74 bolt make it pretty easy to do just butthe correct ar mag then a 223 AK mag can be made to work or a 5.45 mag. I think a ak 74 bolt was the right size I forget right now. I was going to open up a bulgy 223 bolt at the time because it had a spring loaded pin.
PERSONALY I WOULD JUST BUILD A 6.5 GRENDAL AS IT SEEMS TO BE A BETTER ROUND.
do a search there are several threads here on doing one.