The U. S. Military is set to adopt a new rifle and LMG round, along with rifles and machineguns. It is the 6.8x51 SIG, known as the 277 Fury for us civilians. It is a composit case with a stainless steel case head with a brass body and is said to be capable of 80,000 psi. Does anyone know if this case is reloadable?

it's supposed to be, and Sig is supposed to be making [or having made] dies for it.
if it ever gets here.

in the meantime you can buy a new 270 Winchester and check out the ballistics you'll be using later.

Non-composite commercial ammo is supposed to be offered at a reduced pressure/performance. Probably fine, since most commercial rifle actions consider 80,000 psi a proof load…



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What kind of suppressor will work at 80,000 psi?

All of them; realize that the high pressure is only at the breech end; at the muzzle is is far less. Pressure curve, called that for a reason.
As for reloadability; also realize that the conventional, all brass case civilian version, will not provide any increase in performance above any other cartridge of it's size, and will be a big waste of time and money.
You need the steel head and special primers to get the high pressures.
As I have said before, it is easy to get 100K psi. out of a firearm; you need steel cases and electric screwed in primers. Like we use in the M256 120mm tank cannon. Nothing special about the gun itself.