I believe that’s already been done. Sig is selling the .277 Fury (civilian name of the same round) in a conventional brass case, naturally, it is loaded to significantly lower pressures. Much more in line with a 7.62X 51.
Full pressure round:
Elite Bonded Polymer Tipped Ammunition
www.sigsauer.com
Conventional brass case:
Elite Match Grade FMG Ammunition
www.sigsauer.com
Sig has offered the rifle for sale, but it ain’t cheap. I think it was a bit over $3000 just for the rifle, and if you wanted to suppressor, add another grand. I don’t see any for sale in the new caliber right now, but it is this platform, currently available in 7.62x51:
The civilian version of the U.S. Army's new XM7 rifle.
www.sigsauer.com
Nobody’s talking too much about the details of the optic system, which was contracted out to Vortex. From the pictures, you can see a low, powered variable optic with a red dot on top. It looks like a pretty capable set up, and there are rumor to be some features like automatic ranging, and management of round count, among others.