The new 3 piece case is very likely only a small improvement over Russian made coated carbon steel case ammo (currently available in 6.72 x 51,
https://www.ammunitiontogo.com/prod...0rds-308-win-red-army-standard-150gr-fmj-ammo). And once production is set up, full steel cases are cheaper than brass instead of 3 piece that are probably triple the cost of brass.
From a pressure retaining standpoint, a full carbon steel case can easily be made adequate for 80 ksi. Without the mechanical joint, I would expect slightly higher case capacity.
The only real advantage of the SIG case is probably corrosion resistance.
Because they are using my tax dollars for this boondoggle, I wish that they would produce this new round in the cheaper full steel at least for training use. Even though it makes tons of sense, they probably wont do it since it would seem to admit that the Russians "got it right" before we did.
For reloading, the SIG brass should reload just fine. With the higher yield strength of the stainless they are using, the base should not expand much if any on firing.