gatnerd said:

Namely, the M14 (and later the Battle Rifle in general) fell out of favor due to the weapon and ammunition being deemed excessively heavy, relatively low capacity vs enemy weapons, and harsh recoiling. And that was when the weapons were ~10.7lbs loaded. 

If people are complaining about a harsh recoil, more mass is a good thing, because physics.

if you cuold make a durable 762/6.8 gun which weighed only 2.9kg, would the recoil be very harsh?>

smg762 said:

if you cuold make a durable 762/6.8 gun which weighed only 2.9kg, would the recoil be very harsh?>

https://www.omnicalculator.com/physics/recoil-energy

graylion said:

If people are complaining about a harsh recoil, more mass is a good thing, because physics.

That is a bit simplistic.  There is a difference in total recoil and how it is perceived by the shooter.

I recall that the Beretta-True Velocity RM277 had a more sophisticated recoil reduction system than the SIG.  I think it was along the lines of the system being used in the  XM250, essentially a recoiling barrel/inner-receiver isolated from the main receiver by a damper.  The longer barrel of the bullpup also allowed a less energetic cartridge to be used with less energy left to create rocket thrust.   The SIG XM5 does not have any recoil-reducing features.  I was obvious early on that it would have highest felt recoil.   I don't know if merely adding a recoil pad to the buttstock is considered an option since traditionally the butt of the rifle is expected to be used as a weapon itself.

One of the issues with a competition like used for the NGSW is that the winner is chosen to be used largely "as is".  It is unlikely that only one of the competitors would have ALL of the best ideas.   From an engineering standpoint, it would make a lot of sense to develop another generation of weapons using the best of the ideas from the previous submissions.  For example, True Velocity claims that their polymer case could handle 80,000 psi.  If indeed that is true, it is entirely possible that the wrong case technology was chosen simply because it was submitted with the preferred rifle design.

nincomp said:

One of the issues with a competition like used for the NGSW is that the winner is chosen to be used largely "as is".  It is unlikely that only one of the competitors would have ALL of the best ideas.   From an engineering standpoint, it would make a lot of sense to develop another generation of weapons using the best of the ideas from the previous submissions.

Absolutely this.

Really I think what would make the most sense is figuring out the case technology and cartridge, then having a new competition where all the manufacturers are given the cartridge (whether its SIG's 6.8 hybrid, TV's neckless polymer, or perhaps a thin wall stainless steel design ala FN .264) and they each design a weapon system around that common cartridge.

And the rifle and LMG competition should be separate, so Company A might have the best Rifle design and Company B might have the best LMG. 

could you have a steel case like the FN, but with a SIG style steel base, to allow high pressures too?  or combine the steel base with a polymer case

The True Velocity polymer case already has a steel base.  It would be possible to make a two-part steel case, but that would likely add cost.  It would probably make more sense to just design a one-piece steel case that could handle higher pressures.   

At this point in time, it is unclear whether raising max chamber pressure is the best option.  There are advantages, for example, more work can be done in a shorter distance, meaning shorter barrels for the same velocity, but there is not yet a lot of experience to know the tradeoffs.  Some potential downsides are: more expensive materials, reduced service life of components,  significant weight increase and sensitivity to dirt, sand, snow, etc.

YouTube

Does The US Military's New Combat Rifle Kinda Suck?

Today we take a look at the military's new combat rifle, the XM7.Be sure to save 25% at Sylvan Arms with code "Brandon"Thanks to SDI! Again, it's SDI.edu for...

He mentions several issues with his 13" 7.62x51 version.

-HEAVY. Whereas the NGSW was quoted at 8.38lbs, he says his 7.62 13" clocks in at a whopping 8.9lbs. SIG themselves list the 13" 7.62 at 8.6lbs. Whether this means the NGSW will also be heavier is unknown, but SIG's past issues with the MCX 5.56 platform has been one of ever increasing weight. 

-Charging handle is very stiff. The Spear uses a unusual, very long and skinny recoil spring. He describes the T-handle as borderline unusable, while the side charging handle is very stiff. Much stiffer than the 7.62 SCAR 17.

-Magazine over-insertion. This one is surprising - a too firm insertion of the magazine will cause it to over insert and jam the weapon, preventing the bolt from being able to close / chamber a new round. From the video this happens with not all that much force either; well below the level of force one would expect an adrenalized soldier to use in a firefight. This is probably easy to solve, but until it's solved its a potentially lethal flaw. 

Recent twitter post from PEO Soldier

https://twitter.com/PEOSoldier/status/1661454518435848193

PdM Next Gen Squad Weapons recently took delivery of #XM7 Rifles and #XM250 Automatic Rifles for Production Quality Testing. Testing has begun and will finish in August. Be sure to check back for updates as we progress through PQT. This summer is really heating up!”

Potential design flaw for NGSW XM7?

Recently its been discovered that the SPEAR-LT (5.56 civilian/leo version of 6.8 SPEAR XM7) has issues with barrel shifting upon load / impact.

Basically if lateral pressure is applied to the barrel it will lose zero - and stay off target even once the pressure is no longer applied. Ie you whack the barrel going in a door, the barrel can get canted to the left and stay a bit canted.

Why is unknown yet, but most likely culprit is some flaw in the barrel to receiver interface.

YouTube

SIG Sauer Firearms MCX Spear LT Barrel Deflection PART THREE

This is the 3rd and FINAL installment of the MCX Spear LT and the barrel issues that we saw. In this video, we explore MCX barrel deviation and provide valu...

2nd source:

https://www.instagram.com/reel/CsmmB6-tnFa/

Claim that this is a 7.62/6.8 SPEAR with same issue (but little further context given)

https://www.instagram.com/reel/CsrOkiwoKup/

Google drive detailed Analysis (excellent)

https://drive.google.com/file/d/17d-jDJePHyNIDEIONoofD7VI7Ys8qJfk/view

Excerpt; problem seems more acute with left pressure vs right

And another test with near identical results