gatnerd said:

SIG's base is Stainless Steel, then the body of the case is brass.

I should know better than to rely on my memory these days... 

I remember thinking that Emeric's neckless polymer case from a decade or so ago was the way to go and seeing it realised I still think that. Enough in common with existing designs to not frighten the conservatives (like me) and a significant improvement in performance. 

Great find Stan.

So that seems to confirm that the TV 6.8 can be pretty easily adapted to existing 7.62 weapons. 

That is can be adapted to the lightweight, Constant Recoil KAC AMG is especially promising.

Assuming weapon and cartridge perform as good as they look, that would be a hell of a combination. 

Well its confirmed.

SIG's "20% lighter" is lawyering the contract; 23% lighter then .270 WSM brass...

https://soldiersystems.net/2021/01/27/sig-ammunition-produced-rounds-of-6-8x51mm/

If that's actually compliant to the RFP, it's only because the RFP was shockingly badly written.  It should never have been defined as "20% lighter" unless there was an actual baseline cartridge to compare against that was actually in service use, like 7.62x51.

"So what I told you was true, from a certain point of view." - Obi Wan Kenobi,  Star Wars: Return of the Jedi

The whole thing just seems insane to me.  Or maybe I am nuts, who knows. 

7.62x51 is already losing a fair bit of velocity shooting out of a 16" barrel.  Cranking the pressure to 80k psi means you are probably losing a crapton of velocity out of a 16" barrel.  Maybe I am doing the math wrong, but a 16"/40cm barrel of 6.8mm caliber is going to have an internal volume of roughly ~14.5cm3.  Assuming the same case capacity as .308, 3.6cm3, that is only 4x the volume of the case, 5x including the case itself.  So even assuming an ultra fast burning powder to achieve that 80kpsi, all the combustion happening in the case itself, you are still going to have an exit gas pressure of 1/5 of that, or 16,000psi.... which if I recall correctly is like a 6-8" barrel on a 5.56, and we know how efficient and pleasant that is. 

Plus that pressure has got to heat up barrels fast, and I bet the cookoff threshold is going to be super low.  It will be loud as hell, and yeah you can mount a suppressor but that only exacerbates the heating problem: there is much more internal surface area absorbing heat vs external surface area radiating it.  And how much suppressor would be required to get the sound down to the level of a naked 20" 5.56 exiting at 4-5k psi.....I'm tired of math though. 

All this for something not producing any more energy than than a 70 year old AR-10, with close ballistics to .308 (at least with good ammo), and saving maybe a pound-ish of ammunition weight per soldier load, maybe less vs. steel case .308.  It seems utterly bananas to me, other than as a way to spend a lot of money, then get some people killed, then time to spend some money again. 

JesseH1234 said:

7.62x51 is already losing a fair bit of velocity shooting out of a 16" barrel.  Cranking the pressure to 80k psi means you are probably losing a crapton of velocity out of a 16" barrel.

Per the SIG 6.8 Briefing awhile back:

SIG Rifle 13" = 2850fps

SIG LMG 16" = 3000fps 

A pretty big bump in velocity for 3"; +50fps per inch. 

Assuming that held true, we'd expect 3200fps from a 20" barrel. Probably closer to 3150fps as velocity increase would likely get lower as barrel length increases due to drop off in bore pressure.