Military Guns and Ammunition

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This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons.

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NGSW Reset / Change in Direction   General Military Discussion

Started 16-Nov by Guardsman26; 13203 views.
In reply toRe: msg 20

From: nincomp


What would happen to the 6.5 Grendel if it used a Sig case and ran at 80Kpsi?  Would it match the 6.5 Creedmoor's performance?  Beefing up an AR15-style rifle has been done before.  At one time AR15-based rifles were made for the WSSM cartridges (Olympic Arms?), and people like Harrison Beene (AR15Performance) sold some AR15-based rifles that used cartridges made from shortened 7.62x51 case and later, 6mm Dasher cases.  These weapons needed a larger diameter bolt and a corresponding larger diameter barrel extension, but that just took some CNC equipment.

How about an 80K psi 6mm Optimum (or 6.35 Opt).  Would it be worth the trouble?

  • Edited 18 November 2021 9:00  by  nincomp

From: poliorcetes


Excuse me for answering again: Why do you think textron is out? What is your guess (or info) about the reasons?

I just cannot figure out how an unsolvable barrel feeding problem would haven't been detected during 20 years


From: Guardsman26



I’m sorry I have no definitive facts on why Textron withdrew from NGSW beyond what has already been stated. I guess they told the Army they had fixed the previous issues, but the intensity of the testing for NGSW showed otherwise. 


I don’t think SIG set out to mislead anyone. They set out to meet a requirement and to show they could meet with a solution that was more robust and lighter than equivalent legacy all brass option. In other words, if SIG’s contender creates a system weight problem and increases the infantry soldier’s weight burden, the problem may be the requirement more than the solution.  

My view is that the original NGSW requirement was bound to result in a system that increased the weight burden. Ultimately, selecting the right future calibre and weapon is about agreeing what requirements to compromise on. If the Army doesn’t like what’s requirements have produced, all it needs to do is dial them back. For example, reducing the body armour defeat range to 300-400 metres, will allow a lighter cartridge. 

FWIW, I still think your 6 mm round of 20+ years ago was bang on target. If NGSW produces something within the same ball park, it will haven a resounding success.  


From: Gr1ff1th


But SIG's solution weighs more in almost all cases, along with the manufacturing difficulty and expense compared to to TV cases, I just don't see what it has going for it, and I'm highly skeptical of everything you've said so far, I don't know what you have to gain by misleading this forum, I thought we tried not to do that here 


From: gatnerd


Guardsman26 said:

I don’t think SIG set out to mislead anyone.

I dont think they are trying to mislead, but SIG definitely lawyered their interpretation of the weight reduction requirement. 

The NGSW called for a 20% ammo weight reduction over the cartridges brass equivalent. 

Most believed this to mean that the goal was some sort of lightweight case technology that would produce a cartridge 20% lighter than a brass case version of that cartridge. Ie a aluminum or polymer 6.8x51 thats 20%+ lighter then a brass 6.8x51.

SIGs position is that they have achieved a 20% weight reduction, because their 6.8x51 cartridge produces 270 WSM ballistics in a 7.62 sized cartridge. Since that smaller cartridge is lighter then a .270 WSM, they have achieved a weight reduction, even though their steel/brass 6.8x51 is nearly the same weight as a brass cased 6.8x51 would be (or nearly identical to actual 7.62 M80A1 brass currently issued.)


From: DavidPawley


Weight reduction cf 7.62x51 was a requirement of NGSW.

SIG is attempting to bullshit their way past their actual weight increase by claiming a mythical reduction compared to a ballistic equivalent that doesn’t actually exist.

You can stop trying to spin it positively.

As for your inside source, names or it didn’t happen. Chatham House rules are for liars.


From: EmericD


Guardsman26 said:

SIG's hybrid case is 10-15% lighter than an equivalent brass case. BAE Systems in the UK is working on an all-steel 7.62x51 mm case that reduces weight by 20%.

The nominal weight of the all-seel (XC-18 f) 7.62x51 mm case manufactured in France during the '60s was 9.82 g, so the SIG hybrid case is in the same range (but could sustain 80,000 psi).

I thought that the US wanted at least a 20% weight reduction for the complete cartridge, and a 10-15% weight reduction of the case will reduce the cartridge weight by only 5-8%...


From: poliorcetes


Thanks for the answer.

I find really difficult to accept that Textron would offer seriously a product with unsolvable and unacceptable precision problems and that they would do that after 20 years. I mean, if barrel engagement was such a problem, it should have been detected  quite before reaching a TR level 5 or greater.

Besides, there were several other case designs that didn't seat the bullet in contact with the chamber before ignition and such precision decreasing problem was not mentioned AFAIK

If finally there was a problem with CT design, then it should be a legal prosecution, since it was delivered at the end of an entire R&D program 

I'm just baffled about what textron's bet was really about


From: nincomp


To be honest, now that we know that Sig's hybrid case can tolerate 80K psi, I would like more work to be done on the polymer case design to see if the accuracy problem could be solved.  If weight reduction is indeed an important goal, the Sig case could be used as a baseline and other designs should try to beat it.*  Maybe even throw in an all-steel case as well.

Just looking at the photos of the neck-less polymer round, it is not difficult to imagine that the bullet could become misaligned with the bore.  It may not even take rough handling, since the significant lateral forces generated by normal cartridge feeding may be enough.   This problem is certainly magnified with the amount of leverage given by a long ogive.  I wonder if alignment would be a problem with the existing M855A1 or M80A1 which have a short ogive and a relatively long shank.  Then again, the problem may only present itself when the cartridge is fed into a hot chamber, which is more an issue of polymer properties.

I would very much like TV to have the chance to make improvements.  There are a couple of issues that I would like to see investigated:

1) Determine if the alignment problems could be solved with the long-ogived style of bullet used in the NGSW trials.  I would imagine that this would mainly involve changes to the case itself.  Possibly moving the bullet farther foreword to expose more of the shank would help.  This way, the bullet itself would provide the initial alignment.   Possibly the way that the bullet is gripped in the case should be investigated.  Maybe a short neck could be added to provide more support for the bullet and improve the alignment of the case itself in the chamber.

2) Determine if a change in the geometry of the bullet shape would provide improved alignment.  Others have mentioned the location of the center of gravity.  Maybe even increasing the length of the shank would help.  There are commercial hunting bullets in the US made by "Cavity Back Bullets" that, as the name implies, have a hollow cavity in the back of the bullet.  This to allow a longer shank without reduced propellant capacity and, supposedly increase the BC of a given weight copper alloy bullet.**

* I think that Sig made a tactical error when introducing their Hybrid Case.  To demonstrate weight savings, they should have created and exhibited cartridges that matched the performance of existing 5.56x45 or 7.62x51, but at reduced weight and reduced bulk (smaller cases).

** Certain States in the US now require the use of lead-free bullets for hunting.  This has prompted competition to develop lead-free bullets that attempt to match the ballistic performance of their lead-cored predecessors.   Here is a link to the purported advantages of the Cavity Back design.

  • Edited 18 November 2021 10:28  by  nincomp

From: Gr1ff1th


TV cases do not have to be neckless, when they are in conventional form they essentially function as normal ammo, except with 26-30% weight reduction, superior thermal properties, more efficient case geometry resulting in a 15% reduction of powder load for equal performance, simplified manufacture etc.

According to EmericD, the GD gun has a barrel extension to support the bullet, and is not suffering from any major accuracy issues according to him (this was also supported by G&A magazines testing), although some edge cases were noted with regards to front heavy bullets in some cases.

You are probably getting confused with the conjectured CT/Neckless accuracy issues, which was partially started by my (mostly) baseless speculation about the rumored exit of Textron (which has still yet to be confirmed), In reality the Neckless TV case is still capable of 3-4 MOA from an unmodified gun, and 1 MOA from an adapted gun, and my comments about accuracy issues with CT ammo is in reference to the action of the gun, not the cartridge, because when the cartridge was tested from a test stand and fixed chamber it was a <1 MOA system, and when fired from a perfectly aligned sliding/rising chamber it is also a 1 MOA system.

The most burning question is whether sliding/rising chamber firearms are suitable for military use, because if they are then CT ammo is the way forward, if they are not, then TV ammo is the way forward, in no paradigm is SIG's Frankenstein cartridge the way forward, It is too heavy, too complex to manufacture, and likely too expensive, compared to it's competitors.

On a side note I still would like to see TV demonstrate an 80KPSI cartridge and rifle, because they say the can do it, and I believe them, but I still would like to see it actually done in real life.