https://en.wikipedia.org/wiki/.277_FURY
GREATLY OUTPERFORMS the 6.5 Creedmore by running 80,000 psi in a steel headed, brass sided 3 part composite case that weighs much less than a solid brass case and is FAR CHEAPER to make. This sounds like where guns are headed ---- much much higher pressures contained in stainless steel composite cases.
Looks sorta like a .270-08 don't it? Note the option exists to stamp the body sides out of "soft" stainless with the steel head still being a harder material. Such composite rounds can run on up to 100,000 psi if the gun's action and splines/lugs can take it. A point of reference here, a .223 proof round runs at 82,250 psi in a SAMMI spec chamber so this isn't completely unknown territory ..... and the Stoner designed AR action can indeed take it.
This is a presentation of both the round and the sniper rifle from Sig Sauer.
https://www.youtube.com/watch?v=8GvZth5ALw4
And this is a SAMMI style drawing of the case outer dimensions.
https://en.wikipedia.org/wiki/File:....MI_diagram.png