Gr1ff1th said:

why do so many people in this community (firearms) act as if current barrel technology is the be-all end-all, as if it would never improve, when in reality it HAS advanced, and now has matured to the point where you have people repeating the tired old "I bet these NGSW rifles will be barrel burners, they'll be useless after 2K Rounds!" being proven wrong

Well really prior to this testing with NGSW, the firearms community hasn't been able to see a 'overbore' max performance round out of a military grade / next gen barrel. 

All these cartridges (xyz super fast) were in the past fired from button broach rifled match grade boltgun barrels, which while extremely accurate are not that durable, and did show noticeable degradations in accuracy within 1500-2k rounds. Absent proof that better results were possible, it was prudent to plan for the worst and look at more modest cartridges rather then betting on a moonshot. 

The real question for me is whether SIG is using a true 'next gen' flow formed super alloy barrel, or if they are just using a Cold Hammer Forged 4150 barrel with chrome lining, or perhaps a CHF Chrome lined barrel using H&K's 416 barrel steel. 

If they're getting 12k rounds from CHF Chrome lined steel, then really the world is wide open for the next generation of high velocity cartridges. 

gatnerd said:

Was any indication given to confirm the 135gr @ 3000fps general performance we've seen published? Or is there the chance that those specs in and of themselves are also a "smokescreen"?

It seems that the "135 gr @3000 fps" is what the TV ammo is achieving with a lathe turned copper bullet (as shown in G&A article) or with the 135 gr SMK bullet.

That doesn't mean that the XM1186 "GP / EPR" bullet is 135 g @3000 fps, nor than the XM1184 "SP / ADVAP" is 135 gr @3000 fps...

Gr1ff1th said:

Maybe Emeric should re examine his GPC paper, specifically his conclusions about bullets in the .243"-.236" range now that this is known Edit : Although I think his issues with those calibres were his Relative Suppression Index, and his heat flux measurements, which probably could be revised now

I did it in 2019 but didn't had the time to finish it / publish it yet.

The main driver for the review was that I previously focused on a 2.8" action length, but my current views are that a GP cartridge should be put into a GP rifle, and you can't make a GP rifle around a 2.8" action (unless you plan to enlist only soldiers above 175 cm).

Given the size distribution of soldiers, you "should" built your GP rifle around a 2.26" action (or nearest offer), and a slender .264" bullet will simply eat too much space, unless you are using a very fat CT case.

So my current views are that within the 2.26" action length, something ballistically similar to the 6 mm ARC, loaded with a ~95 gr bullet, is all that is needed. The Chinese 5.8 mm is also a very good contender for the GPC job.

1. Excuse me for the question, because probably it has been made more than once here but my memory fails just too much lately. Why do you think SiG decided for a steel + brass case instead of a pure steel one? I assume that there is a reason that compensates higher expenses and complexity but I cannot figure it out

2. If M1186 design ends into a "broad belt" factor (belt as the part of the bullet that is in full contact with the bore, I don't recall the name in English), even if chamber/barrel alignment is not as precise as it would be desirable... Could it compensate such disalignement and exit the muzzle properly oriented and with enough gyro stabilization?

Merçi in advance as always

EmericD said:

specs in and of themselves are also a "smokescreen"? It seems that the "135 gr @3000 fps" is what the TV ammo is achieving with a lathe turned copper bullet (as shown in G&A article) or with the 135 gr SMK bullet. That doesn't mean that the XM1186 "GP / EPR" bullet is 135 g @3000 fps, nor than the XM1184 "SP / ADVAP" is 135 gr @3000 fps...

That does open up some interesting possibilities in terms of what 'actual' performance is. 

TV has repped a 135gr projectile, SIG has repped a 135gr projectile, and Cobalt/Mars repped a 140gr projectile. All in the 3000-3200fps. 

But, that could have been based on launching the copper lathe turned 'surrogate' projectile, which as I recall was offered by the gov as a technical drawing for the companies to make for themselves. 

It could be the surrogate projectile is designed not so much to replicate weight, as volume and projectile shape...

At which point we could see the Steel EPR in the 125gr weight class, and the Tungsten AP could be quite a bit heavier ie 155gr + zone. 

Oy, now I feel like we know less then we did a week ago. 

gatnerd said:

It could be the surrogate projectile is designed not so much to replicate weight, as volume and projectile shape...

That doesn't make sense to me. 

For weapon development and function testing, I'd think surrogate ammo would need to have the same bullet weight (and muzzle velocity) as combat ammo.

Plus, the shape of the GP bullet is clearly not the same as that of the machined copper solid (which, IIRC, has only been reported in TV "commercial" loads).

stancrist said:

Plus, the shape of the GP bullet is clearly not the same as that of the machined copper solid

Perhaps its more inline with the shape of the Tungsten AP projectile? 

https://imlive.s3.amazonaws.com/Federal%20Government/ID5041233544762060809463086928281536454/NGSW_Industry_Questions_&_Comments_152_-_281_Part_2.pdf

Then theres this:

https://soldiersystems.net/2018/10/04/161298/

* General Purpose (GP) per Drawing titled “6.8MM GENERAL PURPOSE (GP)”. The GP cartridge provides all-purpose solutions for combat, limited training, and basic qualification.
* Surrogate per Drawing 13072652. The surrogate cartridge is designed to mimic the behavior of combat projectiles from a weapon design standpoint. Surrogate projectiles may not be completely representative of the final combat ammunition configuration which are expected to vary during development. Surrogates are intended to be a close replacement shape of the final combat rounds.

This seems to suggest Surrogate is different then the GP projectile in weight and or shape.

Which leaves open the chance that AP load is fairly different in weight and shape then the GP EPR, as if they were more or less the same there would be no need for both to be tested. 

gatnerd said:

* Surrogate per Drawing 13072652. ... Surrogates are intended to be a close replacement shape of the final combat rounds.

This seems to suggest Surrogate is different then the GP projectile in weight and or shape.

Concur re shape.  The "Industry Questions & Comments" explicitly states that the GP and SP projectiles are different in shape.

However, I do not see anything in the items you quoted which indicates that the GP and SP bullets necessarily differ in weight.

YouTube

SIG NGSW 6.8mm Expert Interview

Full interview with Jason St. John the SIG expert on the MG68 Next Generation Squad Weapon. This future machine gun with replace the US Army's 5.56mm M249 Sq...

Notes:

-SIG has a GPMG version with QCB and handle to allow barrel changes like 240 in the field

-8:50 shows good cutaway of how recoil buffer works

-Claim case can go 2x the pressure of brass, only ~10% of its extra capability used (ability to grow in power for future needs)

-Suggest weapon could also handle even higher pressures without needing big changes

-6.8lmg backwards compatible with 6.5C and 7.62x51 with just a barrel change

-Equal or less recoil to M249 SAW

....

The ability to grow in power within the current cartridge is very interesting, and does speak to the SIG cases advantage over the TV case. 

....

TV is 'moderate' (below 80k) pressure + longer barrel; sensible today but leaves limited room for growth in performance in coming decades. 

...

SIG 80kpsi + short barrel leaves option of say, defeating future Level V armor by going with a longer barrel to increase velocity, and 'Level VI' armor by going Long Barrel + Higher (100kpsi +) in the future. Of course thats predicated on a similarly linear development in armor tech. 

But so far this was my favorite video on SIG's NGSW because it got more into the smaller details that we'd be interested in. 

Am i right in thinking that polymer case requires thicker walls, and combining it with 80k PSI would need even thicker walls?

If one had a polymer 80k 5.7x28, would it be substantially larger than the original 5.7?