The 6.5 Creedmoor case has less taper and a sharper shoulder than the 7.62x51 and 260 Rem.  Have these presented any problems in weapons function?

gatnerd said:

6.5 Creedmoor is a 62kpsi cartridge, and 6.8 NGSW is much faster out of 14-16” barrels due to being a 75-80kpsi cartridge.

The commercially available 6.5x48 mm Creedmoor cartridge shoots at 62,000 psi. But insiders tell me that the military version developed by SOCOM and incorporating an EPR bullet, shoots at 65,000-70,000 psi. The 6.5 mm bullet mass is 105 grains (6-7 grams) versus 120 grains (8-9 grams) for 6.8x51 NGSM. So performance should be almost as good. 

I am going to suggest that 6.5x48 mm Creedmoor SP penetrates Level IV plate at 300 metres, while SIG's 6.8 mm cartridge does so at 500 metres. If the 6.5x48 mm Creedmoor can deliver this level of performance using standard brass in a cartridge with a lower weight, and less recoil, it will offer a better set of compromises that could weigh in its favour. At the very least, I expect the excellent work being done by SOCOM to influence the final NGSW standard. 

Also, SOCOM is also fielding a weapon in 6x39 mm ARC, also with an EPR bullet. If you extend the ARC case to 45 mm and put more powder behind it, it may be possible to deliver respectable Level IV penetration in a cartridge close in weight to 5.56 mm but that overmatches 7.62 mm beyond 300 metres.  

@nincomp

No issues with belted 6.5 mm CM.

Guardsman26 said:

I expect the excellent work being done by SOCOM to influence the final NGSW standard. 

In what way(s)?

Guardsman26 said:

Also, SOCOM is also fielding a weapon in 6x39 mm ARC, also with an EPR bullet. If you extend the ARC case to 45 mm and put more powder behind it, it may be possible to deliver respectable Level IV penetration in a cartridge close in weight to 5.56 mm...

A 6x45 ARC would weigh ~16 grams.  That is a little closer to 5.56x45 NATO than 6.5x48 CM at 18 grams, but not by very much.

And unless completely new NGSW-R and NGSW-AR of reduced size would be developed, I'm doubtful it would be worth doing.

I think there is a growing consensus among the US Army user community (especially SOCOM) that NGSW has “thrown the baby out with the bath water.” By this I mean that by setting such a high requirement for Level IV armour defeat at 600 metres, it has re-introduced all of the disadvantages that led to 7.62x51 mm NATO being replaced by 5.56x45 mm NATO. Chief among these is that soldiers will have less available rounds for a given weight of ammunition carried. The cost implications (four-piece (ammunition, increased barrel and parts wear, expensive exotic fire control unit etc.) ,   the logistical implications, the training burden, and most significant of all, the dismounted infantry soldier’s weight burden will increase. So, rightly, SOCOM, is trying to get RDECOM to refocus on priorities other than target defeat at 600 metres. Maybe 300 metres is enough, if it overcomes some of the other disadvantages. I believe SOCOM will bring a healthy dose of realism back into the program so that NGSW makes sense. 

Guardsman26 said:

I think there is a growing consensus among the US Army user community (especially SOCOM) that NGSW has “thrown the baby out with the bath water.” By this I mean that by setting such a high requirement for Level IV armour defeat at 600 metres, it has re-introduced all of the disadvantages that led to 7.62x51 mm NATO being replaced by 5.56x45 mm NATO. Chief among these is that soldiers will have less available rounds for a given weight of ammunition carried. The cost implications (four-piece (ammunition, increased barrel and parts wear, expensive exotic fire control unit etc.) ,   the logistical implications, the training burden, and most significant of all, the dismounted infantry soldier’s weight burden will increase. So, rightly, SOCOM, is trying to get RDECOM to refocus on priorities other than target defeat at 600 metres. Maybe 300 metres is enough, if it overcomes some of the other disadvantages. I believe SOCOM will bring a healthy dose of realism back into the program so that NGSW makes sense. 

one can hope. I also wonder what the lessons from UA will be. Back to maxims in 7.62x54R?

Guardsman26 said:

I believe SOCOM will bring a healthy dose of realism back into the program so that NGSW makes sense.

Sorry, but I don't see that happening.  SOCOM wants 6.5x48 CM, a cartridge which is as big -- and nearly as heavy -- as 6.8x51 SIG. 

And switching to 6.5x48 CM would give zero reduction in size or weight of the weapons, and zero increase in magazine capacity.

If 6.5x48 mm CM is fired at standard pressures, with a performance more or less equivalent to 6.8x51 mm, it would allow a polymer version to be created. This would offer a significant weight saving. But as you note, it would not increase total rounds carried relative to 6.8x51 mm. 

However, more fundamentally,, SOCOM is trying to drive a more realistic requirement. This is significant, but whether it leads to lead to an ammunition derived from 5.56 mm or 7.62 mm, hopefully it will not increase the weight burden.. 

Guardsman26 said:

If 6.5x48 mm CM is fired at standard pressures, with a performance more or less equivalent to 6.8x51 mm, it would allow a polymer version to be created. This would offer a significant weight saving.

I mean, they had a polymer cased cartridge that fired at standard(ish) pressure of 65kpsi - the 6.8TV. They went with the high pressure, heavier metallic case of the SIG. 

At 62kpsi (or even 65) the velocity is much lower - about 300fps lower - then the 6.8 SIG from a 16" barrel. 

6.5C is a fine cartridge, but I dont see it either providing comparable performance to 6.8 NGSW, or solving most of the issues (weight, weapon weight, limited mag capacity) with NGSW. 

gatnerd said:

6.5C is a fine cartridge, but I dont see it either providing comparable performance to 6.8 NGSW, or solving most of the issues (weight, weapon weight, limited mag capacity) with NGSW.

You are absolutely right.  Because of its size, 6.5 CM simply cannot solve any of those NGSW issues. 

And even with polymer cases, 6.5 CM ammo will still be heavier than 5.56 NATO brass-cased ammo.

Let's be clear here, in order to deliver Level IV body armour defeat at 600 metres, NGSW presents several critical disadvantages: 

• The specification is identical to .300 Winchester magnum which is a sniping cartridge
• In order to avoid using a larger cartridge that would increase ammunition weight, the performance is packaged in 7.62x51 mm size case
•  This in turn results in chamber pressures of 80,000 psi
• As a result of this, heat builds-up in the weapon more quickly, reducing barrel and parts life, and battlefield reliability.
• It also introduces significant recoil, making automatic fire more difficult to control.
• Developing a weapon able to deliver this level of performance requires 4-piece ammunition. This is more complex and costly to produce.
• 6.8x51 mm reduces the amount of ammunition that can be carried for a given weight - this reduces hit probability
• Overall system cost is likely to be significantly greater even before you add the XM157 FCU optic and integral suppressor
• Overall system increases the logistics burden
• Overall system increases the training burden 
• Overall system increases the dismounted soldier's weight burden
• All of this extra long-range performance comes at the expense of 0-300 metres performance - and still this remains the critical range envelope

The question raised by 6.8x51 mm NGSW is how important is the need to engage enemy targets at 600 metres? And do the benefits of being able to do so outweigh the clear disadvantages. How often will we need to engage enemies at this range, and how convinced are we that 6.8x51 mm NGSW will be effective versus other weapons we might employ, such as 60 mm, 81 mm and, 120 mm mortars? 

As someone who has worked in military equipment acquisition for 20 years as well as being a former infantry officer, to me NGSW is redolent of very bad requirements writing. I was brought-up on 7.62 mm. But I also have operational experience of 5.56 mm. An infantry section / squad shooting 5.56 mm is consistently better able to to achieve target effect than the same group using 7.62 mm. NGSW isn't just a reintroduction of 7.62 mm NATO, it is a much more powerful round, so I don't expect shooting results to be significantly better even with an optic. 

For these reasons, I believe we need NGSW to have a lesser requirement - arguably to defeat body armour to 300 metres. This will result in an ammo that is more capable than 7.62 mm, but lighter, and without the cost and logistical issues of 6.8 mm NGSW ammunition. 

It appears that SOCOM shares this view. And we are NOT talking about standard 6.5 mm Creedmoor - we are talking about a new specification based on that cartridge fired at a higher chamber pressure so it delivers increased penetration out of shorter barrels. (Gatnerd, your 6.5 mm chart is meaningless in this context).

Let's call SOCOM's 6.5 mm round 6.5 mm Creedmoor SP.  Is it optimised to blanche the conflicting requirements for NGSW? No. Because it still reduces the number of rounds carried for a given weight. Would I prefer a 6 mm round fired at the highest possible velocity in the smallest possible case? Yes. But, if the requirement demands Level IV defeat, and this mandates 6.5 or 6.8 mm, we may have to accept certain disadvantages.  What we can't do is destroy logistical efficiency, increase the training burden, increase the weight burden by adopting a more expensive weapon with more expensive ammo and that has a shorter life. 

Finally, for the sake of clarity, TV polymer ammo is not the only game in town. MAC's technology, which was bought by Nammo, has a working polymer 6.5 mm case that supports 60,000-70,000 psi.