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.

EmericD said:

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.

Hmm. is the 240Lima with its lightened receiver is then out of this game? And what would happen if such ammo by mistake would find its way into, say, G3, SCAR-17, M110 or some other "NATO standard" rifle?

Thanks!

I am also thinking that UA Rambo in the trench - that was no job for a rifle in the first place, that's PDW territory. I get, of course, that in a trench you'd have a rifle. I just don't see it as an argument agains the M5.

mpopenker said:

Hmm. is the 240Lima with its lightened receiver is then out of this game?

I don't think so. A lot of people complained that the FN "Lima" was still overweight and that FN did a lazy job.

mpopenker said:

And what would happen if such ammo by mistake would find its way into, say, G3, SCAR-17, M110 or some other "NATO standard" rifle?

I don't know. Maybe they already tested them in SCAR / M110 / M110A1 and find that they were OK, or it's just for some laboratory / development testing, or simply advertisement.

Anyway, if the 6.8 x 51 mm became a reality, it won't take long for US shooters to wildcat this case to make "hybrid" .243 Winchester / .260 Remington / 7-08s... with the possibility of overloading the ammo and ruining some guns.

EmericD said:

I don't think so. A lot of people complained that the FN "Lima" was still overweight and that FN did a lazy job.

FN did a lazy job with the MAG back in 1958, and everything else is just a similarly lazy continuation.