mpopenker said:

And who said it was something special?

Nobody.
I am just wondering what the problem is if an industrial standart solution delivers the results you mentioned. To me it seems like a really effective approach cost to performance wise.

Came across this interesting slide on Twitter, showing SIG's hybrid 7.62 as an AP round:

https://twitter.com/2805662/status/1628607690430902272/photo/1

Notable aspects of the slide:

1. +500fps claimed (vs what? M80 or M80A1?) That could mean the round is going 3250-3500fps if the +500fps is true.

2. 12% lighter then conventional brass case design. Once again, this is worder vaguely - is that 12% case weight reduction, or 12% cartridge weight production?

3. Projectile is listed as 131gr, whereas the M80A1 is 135gr. Transcription error? New EPR design? Or is this a glimpse of the 7.62 ADVAP Tungsten projectile?

If this is indeed the ADVAP, a 131gr 7.62 suggests the 6.8 ADVAP could be lighter than the 135gr we've been using for our estimates. 

gatnerd said:

Projectile is listed as 131gr, whereas the M80A1 is 135gr. Transcription error? New EPR design?

"The [M80A1] bullet measured 8.48 grams, or 130.87 grains."  Taking a Look Inside the Army's DEVASTATING New M80A1 7.62mm Round -The Firearm Blog

Ah thank you stan, I had forgotten the M80A1 was 130gr / transposed 135gr with all of the 135gr ngsw talk we've had.

So then almost certainly M80A1 is the projectile. Which means if +500fps (seems almost impossible) that would be going ~3500fps from a m240. 

Yeah, I am skeptical of their weight and velocity claims being versus M80A1.

Although the slide shows an M80A1 round, I'd bet they're comparing to M80.

How did they get their accuracy assessed? The standards for the US M4 barrel is 10 shots out of a barrel, in a barrel fixture, =< 4MOA. Did the Soviets use the same testing procedures, or something different?

gatnerd said:

1. +500fps claimed (vs what? M80 or M80A1?) That could mean the round is going 3250-3500fps if the +500fps is true.

The 131 gr bullet seems to be the M80A1, and in order to achieve ~111 inches of drop at 600 yards you need to push this bullet at 915 m/s / 3000 fps which is totally into the realm of the M80A1 cartridge with a ~20" barrel. The powley computer is predicting a MV of 2995 fps @52,000 CUP with this same bullet and barrel length.

By the way, increasing the MV to 3500 fps (or 1067 m/s) will give you ~196 cm of drop at 600 yards, or 77 inches, which seems to be what is claimed on SIG's chart.

Pressure estimates is 71,000 CUP for 3500 fps out of a 20" barrel.

The comparison seems to be between the current M80A1 (131 gr @3000 fps) and the M80A1 +P+ (131 gr @3500 fps).

Not sure if a "5.56 x 40 mm +P+" would be a good idea (because the AR-15 bolt will be probably out of its limitations), but launching a 64 gr / .224" bullet with a C7 of 0.208 at nearly 3400 fps from a 14.5" carbine would be an interesting feature.

IIRC the Soviet era norm for the AK-74 was to have no less than 50% of all shots fired from prone supported position in the 10x10cm square, with several strings of 20 shots each. But I believe only a specified percentage of new rifles from any given batch was tested like that, the rest was just proof-fired and zeroed at the special automated machine.

Today I believe the area is smaller but I'm not sure about the exact dimensions. 

One important factor is that Soviet / Russian steel-cased, steel-jacketed and steel-cored ammo generally has somewhat bigger dispersion than the Western brass-cased and brass-jacketed ammo

However, in my own experience, with a cheap steel-cased and steel-jacketed Barnaul 5.45 fodder and my civilian AK-12 / TR3 rifle I can easily hold those 4 MOA 10-shot groups all day long from supported position, sitting at the bench like this

EmericD said:

By the way, increasing the MV to 3500 fps (or 1067 m/s) will give you ~196 cm of drop at 600 yards, or 77 inches, which seems to be what is claimed on SIG's chart. Pressure estimates is 71,000 CUP for 3500 fps out of a 20" barrel.

I wonder what kinds of legacy weapons can safely and routinely handle this stuff, as, I believe, the standard 7.62x51 NATO is rated at 50,000 CUP

mpopenker said:

I wonder what kinds of legacy weapons can safely and routinely handle this stuff, as, I believe, the standard 7.62x51 NATO is rated at 50,000 CUP

Not a lot of weapon, for sure, but the MAG 58 / M240 will handle this diet, with its fat and heavy receiver borrowed from the M2HB.

The US Army is working on converting some M240 to fire the "+P+" 6.8 x 51 mm, so it seems logical to be able to feed the M240 with "+P+" M80A1.

That could also explain why the full power 6.8 x 51 mm is not fully developped yet and the US Army and SIG are still "fine tuning" the pressure level of this round.