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. 

Apsyda said:

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.

I'd say it's more likely that those were dummy 6.8 NGSW cartridges, that SIG decided to apply its black coating to for easy identification as dummy rounds.

Apsyda said:

The coating looks to be mainly applied to their 'Short Barrel 300 AAC' line.

Yup.  Black cases for .300 AAC Blackout cartridges.  It's kinda poetic.

Apsyda said:

But I couldn't find any pics showing good amounts of wear to confirm that they also expose white looking material underneath.

To my eye, the black case in this photo looks to be a good match.

Testing Sig's .300 Blackout Short Barrel Loads :: Guns.com

Apsyda said:

The coating looks to be mainly applied to their 'Short Barrel 300 AAC' line.

The coating was a request from some "end-users" to easily make the difference between subsonic and supersonic loads (shiny brass = supersonic; black = subsonic).

EmericD said:

       Apsyda said: The coating looks to be mainly applied to their 'Short Barrel 300 AAC' line.

The coating was a request from some "end-users" to easily make the difference between subsonic and supersonic loads (shiny brass = supersonic; black = subsonic).

SIG has gone beyond that original use.  SIG commercial .300 BLK ammo uses black cases on both supersonic and subsonic "short barrel" loads.

Possibly it was answered quite a long time ago but... why 6.8x51 case is not all steel like Russian cases in order to save weight and be much more cheap to build?

poliorcetes said:

Possibly it was answered quite a long time ago but... why 6.8x51 case is not all steel like Russian cases in order to save weight and be much more cheap to build?

I don't know if "all steel" cases will be cheaper, I suspect that the process to build the 2-parts case makes the material cost less important.

As for the reasons that SIG didn't proposed an all steel case, first steel is not a really good material for the case body. You can make a decent all steel case, but it's not an everyday business among Western manufacturers, the process is very special and SIG probably didn't have enough time to develop it during the NGSW competition.

Second, the "high pressure" NGSW cartridge is still under development, as the US Army really want a true lightweight round, so maybe the final iteration will be very different from the things we already saw.

Russians playing with bimetal 'import subsituted' cases for their ELR sniper rifles. They say bimetal manufacturing makes for much better tolerances particularly in the neck area  and is this case comparable to cost of imported brass.

But of course with large sniper cases made in low numbers  , costs are on different plain .

1. Even if steel base + washer + brass body is not so expensive, it also would need a good number of resources in order to make it viable at the manufacturing line. Would such resources be more at hand rather than go to steel only?

2. Is there any clear indication than bimetallic .277 is not going to be the final case for the cartridge? Are there any hints of a less powerful GP variant? 

3. I would assume that any polymer case should reduce slightly the propellant volume. Maybe a less long GP round would compensate it, or maybe it also would pointed out to the direction of reducing muzzle energy since COAL is already be written on stone

Reportedly, some Rangers already getting NGSW:

https://www.reddit.com/r/MilitaryPorn/comments/10a2g7j/rangers_of_the_4th_ranger_training_battalion/