But it's lighter than a cartridge would be to get that performance level from a standard pressure case, so technically it's a lot lighter.

Farmplinker said:

But it's lighter than a cartridge would be to get that performance level from a standard pressure case, so technically it's a lot lighter

Yes thats true, and thats the lawyered interpretation SIG is going with and the Army accepted.

And to be fair, its not without merit.

For 6mm CAKE (85gr VLD @ 3000fps) I had envisioned a 6mm HAGAR sized case, but the sig could do it with a high pressure 5.56 case necked up to 6mm. A real weight and volume savings. 

gatnerd said:

       Farmplinker said: But it's lighter than a cartridge would be to get that performance level from a standard pressure case, so technically it's a lot lighter

Yes thats true, and thats the lawyered interpretation SIG is going with and the Army accepted. And to be fair, its not without merit.

I tried to locate the original PON to see what the actual phrasing was, but had no luck. 

The best I found was a TFB summary, which may or may not be a quote from the PON:

     "Ammunition Weight: 20% less than equal amount of conventional brass cased ammunition"

       US Army Calls for Next Generation Squad Automatic Rifle Prototypes -The Firearm Blog

stancrist said:

actual phrasing

I recall the phrase 20% less then "equivalent brass case," which leads to some question of what 'equivalent' means. 

20% less than brass 6.8x51 case?

20% less than brass 6.8x51 cartridge?

20% less than 6.8x51 ballistic equivalent brass cartridge (ie 20% less then .270 WSSM)?

Regardless, the result is something likely indistinguishable from 7.62x51M80A1 brass to carry. 

whats the approx length of 6.8mm bullets compared with 762

any idea of the weight of GD's, textrons or sigs rifle?

or textrons ammo?

smg762 said:

whats the approx length of 6.8mm bullets compared with 762

smg762 said:

any idea of the weight of GD's, textrons or sigs rifle?

Don't know for Textron, but the True Velocity RM277-R rifle is quoted at 9.5 lbs dry with a length of 29.1 in. (with flash hider) and 32.2 in. with the Brevis III suppressor. Barrel length is 18.65 in.

The quoted MV is 2950 fps for a 135 gr bullet, and the cartridge weight is 17.8 grams. The 100 rds. belt is reported at 4.725 lbs with plastic links, vs. 6.323 lbs for a 100 rds belt of M80 ammo.

An interesting point is that True Velocity 6.8 mm TVC is currently under revision:

https://saami.org/wp-content/uploads/2023/03/Public-Introduction-6.8-TVC-2022-01-28-SUSPENDED.pdf

Also, SIG is proposing a hybrid case 6.5 mm Creedmoor +P+ loaded with a 102 gr EPR bullet launched at 3400 fps... only ~74 in. of bullet drop at 600 yards!

EmericD said:

Also, SIG is proposing a hybrid case 6.5 mm Creedmoor +P+ loaded with a 102 gr EPR bullet launched at 3400 fps

Thats incredible, is that from a 16" barrel?

And its interesting, like the .264 FN we're seeing a pretty lightweight 6.5.

Do you know, is this 6.5 EPR comparable in shape to the 6.8 EPR we've seen for NGSW? Or is it more abbreviated to reduce weight?

If its the same shape as 6.8, makes me think the 6.8 EPR will be a good bit under the 135gr we've seen quoted for surrogate projectiles.