with wider cartridges like the 6ARC, could you some how angle the magazine at 45 degrees to improve prone shooting?

and then somehow use a special feed ramp to get the bullets in barrel

smg762 said:

what was the barrel length on the textron rifle.

IDK.

smg762 said:

did the 556 CT rounds offer any reduction in volume

Here is a 2014 presentation of the 5.56 LSAT.  Main selling point was ammo weight reduction, largely for linked.  37% weight reduction, 12% for volume.

https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2014/armaments/Wed16533_Shipley.pdf

Here's an unusual development:

https://soldiersystems.net/2023/09/18/army-marksmanship-unit-seeks-match-grade-6-8-ammo/

1a. BULLET: .277 dia. 135gr Sierra Match King OTM item or .277 dia 140gr Classic Hybrid Hunter Berger Bullet. End user will accept projectiles not listed if precision dispersion is better than specific projectiles/bullets listed. If an optional projectile is proposed the optional projectile cannot weigh more than 150gr.

....

1f. MUZZLE VELOCITY: ammunition must produce a velocity sufficient to provide Sub MOA accuracy from 16″ Bolt Action barrels & 1.15 MOA or less from semi auto barrels and maintain low SD of MV. Standard deviation of MV should be 13 fps +or- 1 fps (or less) for avg of 30 rds tested at 70F. Actual muzzle velocity shall be a mild velocity ammunition not to exceed 64 KSI from PSI test barrels at Hot temp ranges. 70F degree test barrel & ammunition should produce an avg of 58-59 KSI. End user not specifying specific muzzle velocity.

--> The use of lead projectiles is not entirely surprising for a match grade round. However the insistence that the round be of conventional pressure, rather then the 80kpsi we've seen in most talk about the NGSW, is quite interesting.

Whether this is just match ammo for competition / training, or an indication in a broader interest in a lower pressure loading for 6.8, remains to be seen.

gatnerd said:

The use of lead projectiles is not entirely surprising for a match grade round. However the insistence that the round be of conventional pressure, rather then the 80kpsi we've seen in most talk about the NGSW, is quite interesting. Whether this is just match ammo for competition / training, or an indication in a broader interest in a lower pressure loading for 6.8, remains to be seen.

Since it is for the AMU, that would seem to indicate it is for competition use.  There is no need for an 80kpsi loading just to punch holes in paper targets.

And if it would also be used by snipers for combat, precision shooting would be more important than the marginal increase in terminal effects of 80kpsi.

stancrist said:

And if it would also be used by snipers for combat, precision shooting would be more important than the marginal increase in terminal effects of 80kpsi.

The added velocity is also increasing the hit probability against moving targets, or targets located at unknown distance, not only terminal effects.

Maybe the base of a lead core OTM bullet is not strong enough to sustain the 80 kpsi of the full pressure hybrid ammo? The EPR bullet  is using a copper core inside the tombac jacket, which is less susceptible to plastically deform under high pressure load, and of course the all-copper "surrogate" bullet used also during the development phase was lead-free.

EmericD said:

Maybe the base of a lead core OTM bullet is not strong enough to sustain the 80 kpsi of the full pressure hybrid ammo?

You would know more about that possibility than I.  But whatever the cause, it appears that the 80 kpsi ammo does not meet AMU accuracy requirements.

As I recall, the 135gr Sierra MatchKing was used as a surrogate projectile during development of full-power ammo.  I imagine the AMU tested some of that.

BREAKING: SIG NGSW Prototype Unveiled To The Public (The Firearm Blog)

I used DSEI as an opportunity to find out what is going on with NGSW. 

A number of engineering change proposals for the XM7 have been submitted and are being implemented in the latest LRIP batch. Surprisingly, one of these is the elimination of the forward assist. Eugene Stoner is on film somewhere saying that this is the most unnecessary modification ever made to the M-16  / M-4, and I agree wholeheartedly. See image. 

More importantly, previously reported issues about ammunition accuracy and reliability were a function of the EPR-style bullet furnished by the US Government. This has been re-designed. In addition to a revised 6.8 mm projectile, new 6.5 mm and 6.35 mm bullets also seem likely to be evaluated. So the final calibre could actually change. I am sure that ballistic calculator aficionados among members of this forum will be able to work out the increased penetration offered by a slightly smaller bullet fired at a slightly higher velocity. It's not clear as to what range Level IV penetration will be be achieved. I expect it to be 300 metres, but that is purely a guess on my behalf. 

The most important thing about Phase 2 testing is that it has validated SIG's hybrid cartridge concept. The weapon is more than able to cope with higher chamber pressures. Standard loads will be fired at 90,000 psi. Proof loads will be fired at 120,000 psi, according to a source I spoke to. I was told that a significant  increase in chamber pressure has been common to all small arms development milestones for 200 years. 

The US Army has made it clear that it deliberately set the bar very high with NGSW. It wanted to see the art of the possible, which SIG has amply demonstrated. Now that there is certainty around the ammunition technology and performance envelope, production guns and ammo will be fine tuned to maximise range, terminal effectiveness, reliability and longevity. 

SIG's approach has also been validated by SOCOM's 6.5  mm LICC cartridge developed by FN America. This is also fired at a much higher pressure than legacy ammunition, believed to be 70,000 psi. They are also achieving good results at longer ranges. LICC may ultimately be a science project that goes nowhere, but it seems likely to influence the final NGSW standard.

As reported elsewhere, BAE Systems at Radway Green has its one-piece steel cartridge technology. This can also sustain much higher chamber pressures. It is supposed to have a unique means of lubrication to prevent the case sticking in the chamber after being fired.

Despite my earlier misgivings, I am quietly optimistic about NGSW. If it can deliver the desired step-change in performance while reducing overall weight relative to 7.62 mm, then it will be worth the effort of switching.  

Guardsman26 said:

I am quietly optimistic about NGSW. If it can deliver the desired step-change in performance while reducing overall weight relative to 7.62 mm, then it will be worth the effort of switching.

The trouble is, NGSW is meant to switch from 5.56mm, not 7.62mm.

Switching to 6.8mm will increase overall weight relative to 5.56mm.*

*Worse yet, the switch from 30-rd mags to 20-rd mags will greatly reduce combat endurance.

Saint Kyle of Kenosha demonstrated that Saint Eugene was wrong about the forward assist.

Also wondering if we're going to see some experiments with high-pressure 5.56x45. Just drop in a new bolt, and possibly buffer and barrel, would be very appealing. 70+ grain EPR at 80,000 psi could be interesting.