Although it is difficult to tell from the pictures that I have seen, it appears that the base is a metal insert that extends a certain distance into the case.  I see no reason that this metal section cannot be make more substantial if the chamber pressure is increased.  Some of the weight reduction would be lost, however.  We do not know at this point if this design will be as tolerant of action types as a brass case, however.  In particular, we do not know at what chamber pressure the extraction may begin without damaging the case.  This might become an issue with delayed blowback designs or even with "overgassed" gas-operated systems.

From what I can see, True Velocity uses a steel base with the extraction groove and primer cup, which is inserted into the polymer case. How is this more susceptible to extraction problems than steel cases, for example?

I can think of a few reasons why they might  be designing for lower pressure anyway:

1. Case weight -- if they design for less pressure, the case can be lighter.  They say they're getting a 30% weight savings over brass, while SIG is only claiming 20%.
2. Barrel life -- really high pressure rounds have a reputation for being "barrel burners," although modern metallurgy seems to be solving that for the most part.
3. Improved customer acceptance -- the Army would probably ask a lot more questions about an 80 kpsi neckless composite than they will of the stainless SIG round (which just "logically" sounds stronger) or the Textron polymer CT round (which has a lot of LSAT testing/experience behind it).  

taschoene said:

They say they're getting a 30% weight savings over brass, while SIG is only claiming 20%.

The TV weight saving of 30% is credible, but I am suspicious of the SIG 20%. After all, the most massive part of the case - the base - is still of brass, only the case walls are steel. I suspect that the 20% figure is the saving in case weight - with the overall weight saving being more like 10%. The CT round probably saves around 33% overall.

With the known information in mind, what cartridge architecture do you people think it could accept more pressure? textron, tv or sig?

BTW I would accept what you and nincomp say about steel base insert on tv's case. It's just that since American military branches are quite against bullpup, and that beretta's SAW design is bullpup too and not belt-feed, that I understand beretta's election as a quite strong trade-off

autogun said:

but I am suspicious of the SIG 20%. After all, the most massive part of the case - the base - is still of brass, only the case walls are steel.

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

I agree though; I'm skeptical of the weight savings as well.

I think at best the SIG case is 20% lighter then a brass case.

Whereas the TV complete cartridge is 30% lighter the a brass cartridge (so like a ~70% case weight reduction vs brass case)

Why do all the NGSW  guns have suppressors, is the US planning on giving one to every grunt?

Also whats the energies of the 277 tvcs...is it about 2000ft  lbs like the 7mm-08?

 and wasnt the original LSAT goal to reduce weight vs 556....why did they go with 7mm ammo in 20 round mags?  Assuming the ammo is at least 15 grams, with a rifle thats 3.2kg or higher, thats a big weight increase. Should have gone with a 224 valkyrie.

I read someone (not a SIG employee) who claimed SIG was getting their weight reduction by comparing performance. A conventional brass cartridge would weigh x to achieve the performance specifications; our cartridge achieved the performance specifications at 20% less weight than x. Sounds plausible, anyway.

I agree with Farmplinker.  I think that the 20% reduction that SIG talks about is vs a comparable cartridge like the 270 WSM.  One article I saw said that the existing round is about the same weight as 7.62x51.

smg762 said...

Also whats the energies of the 277 tvcs...is it about 2000ft  lbs like the 7mm-08?

No, considerably more. We have seen numbers of 3000fps with a 135 grain bullet, so closer to 2700ft-lbs, which makes it more like a 270 WSM.  The goal is to penetrate hard body armor at several hundred meters, 600 iirc.  It is to have a suppressor.  As near as I can tell, other goals included less recoil than a .22 rimfire, lighter weight than the average feather, and the abilities to tie the soldiers boots and walk the General's dog.  

USMC is already transitioning to widespread use of suppressors, so it's not surprising that Army could follow suit.