Excellent find! 

Heres both images larger:

The cases to me look one-piece, and are black. 

Combined with this picture being taken at a display booth or office (where one generally doesn't want a belt fed machinegun with live ammo) I suspect these are polymer dummy cases with real EPR projectiles.

...

In terms of EPR, its good to see they are nice and pointy and streamlined, which seems to my eye to match the 6.8 EPR prototype we had seen earlier.

gatnerd said:

The cases to me look one-piece, and are black.

Black?  Oh, great.  Now I'm going color blind.  The cases look gray to me.

gatnerd said:

Combined with this picture being taken at a display booth or office (where one generally doesn't want a belt fed machinegun with live ammo) I suspect these are polymer dummy cases with real EPR projectiles.

The T-Worx post said the photo was taken at AUSA 2022, so I agree that they are almost certainly dummy rounds.

However, they do not look like any polymer cases that I've seen.  They look to me more like lacquered steel cases.

They could be steel.

That said, they are black, or darkest dark grey. Note the dark grey of the MG links - about as grey as normal steel case x39 ammo - these 6.8 cases are much blacker then the MG links:

The appear to be about as black, maybe slightly lighter, then the black plastic that makes up the top of the ammo pouch underneath them. 

If this is some sort of lacquered steel, then it's a new lacquer coating then what we've seen come out of Russia or really anywhere I'm aware of. 

It would also just be odd to use steel cases here, as the sort of soft 'cartridge steel' used in Russian style steel case ammo is not appreciably stronger or that much lighter then brass, and would require completely new cartridge tooling then what the US uses (to my knowledge there is no US made steel case ammo).

If it's the high pressure steel like used in the GD prototype cases, that could be very cool. And those externally look to be one piece, unlike the Shell Shock and SIG cases. 

gatnerd said:

It would also just be odd to use steel cases here, as the sort of soft 'cartridge steel' used in Russian style steel case ammo is not appreciably stronger or that much lighter then brass...

If they are dummy rounds, strength and weight do not matter.

And there is precedent for using steel case dummy cartridges.

WWII, Korea Dummy Training Rounds M1 Garand, Clip, 30-06

The leftmost round has the lacquer chipped away on the edge of the case shoulder. It’s shiny in the shadow and at a different angle to the reflection of the lights on the cases. The cases are not polymer. The exposed metal is silver not brass or white. I’m interpreting it as lacquered steel.

A rather interesting reloading component has showed up; American Reloading often has obscure / military components (for example, the only website I've ever seen offering M80A1 projectiles.)

Now they have .277 Furry / 6.8NGSW cases. Quite expensive at $1 a piece as well; whether thats due to scarcity or due to them being expensive to manufacture, I don't know.

https://americanreloading.com/277-fury/3249-277-fury-sig-primed-hybrid-case-100ct.html

I'm going to email them and ask whether they can weigh one of the cases for us. 

Don't forget the cost of the primer and putting it in the case.

Buy them if you can .i would if i could 

I think we all got excited for naught here.    

Seems to be that SIG sells brass cased ammo with a black coating on it already on the standard commercial market. Should have checked because that kind of casing color wackiness is up SIG's alley. But at least it's more likely that those were Low Pressure 6.8NGSW cartridges, so all brass, that SIG has decided to apply its coating to for XYZ reasons. Over being a new generation of high strength steel cases.

The coating looks to be mainly applied to their 'Short Barrel 300 AAC' line. But I couldn't find any pics showing good amounts of wear to confirm that they also expose white looking material underneath. As the above linked cartridges seem to have white colored wear patterns.

Excellent find man. That seems to settle it.