AMU testing 6.5 based on Carcano case

[stanc]

In case it's of interest, I happened upon a photo of Harrison/woohoo's Carcano-based 6.8x45 cartridge (second from right, below):

[stanc]

Happened upon a notice of solicitation for .264 USA cartridge cases:

https://www.fbo.gov/?s=opportunity&mode=form&id=06d9ea25bb78aaabdc64519390251021&tab=core&_cview=1

[stanc]

From the IAA forum:

"The .264 USA is one of the intermediate cartridges that will be tested in the current lightweight ammunition program, which also includes 7.62x51, 5.56x45 and a new .277, all using polymer cases. The proposed shooting plataform for those two new calibers is a AR-10 type rifle."

[stanc]

From: https://www.bids.tswg.gov/TSWG/bids....B2014_TOS.pptx

Lightweight Intermediate Caliber Cartridges (LICCs)

Load and deliver mature test sample ammunition of 264 USA and 277 USA cartridges with lightweight (threshold); polymer (objective) cartridge cases with Sierra HPBT "MatchKing" projectiles.

Cartridges will function in modified, purpose-built AR-10 rifles and magazines in the semi-automatic and fully automatic modes of fire with and without the use of a muzzle-mounted signature suppressor.

Accuracy: 1.5 MOA (threshold); 1.0 MOA (objective) to 600 m (threshold); 800 m (objective).

[BluntForceTrauma]

Thanks for the info, Stan. For the reader's convenience I note that metric case length for 1.873" is 47.6mm.

Any serious intermediate cartridge will have a high BC bullet, particularly if the AMU has anything to say about it. So, you're welcome, I think we've proved our point.

Of course, they can't just use the 6.5 Grendel, because that would be too easy. Not Invented Here. And doesn't provide the opportunity to sink development dollars into the procurement circus. . . .

[stanc]

Thanks for the info, Stan. For the reader's convenience I note that metric case length for 1.873" is 47.6mm.

You're welcome, John. BTW, "BluntForceTrauma"? Are you trying to tell us something?

Any serious intermediate cartridge will have a high BC bullet, particularly if the AMU has anything to say about it.

Well, the case mouth to bullet tip dimension is approximately the same as that of 6.5 Grendel, so I guess it should be equally able to use high-BC projectiles.

I found it interesting that case shoulder angle is the same as on the old .30-06 cartridge. I would've expected them to not use the steep, bench rest shoulder of the Grendel, but I'm quite surprised to see them revert to such a shallow angle. Shows an emphasis on feeding/chambering reliability?

Of course, they can't just use the 6.5 Grendel, because that would be too easy. Not Invented Here. And doesn't provide the opportunity to sink development dollars into the procurement circus. . . .

To be fair, 6.5 Grendel can't deliver the desired ballistics from the shorter barrels currently favored for infantry rifles and machine guns. It'd be necessary to use 24" barrels, as per Tony's latest brainstorm (See http://www.65grendel.com/forum/showt...l=1#post102078), and that, IMO, is unlikely to happen.

Plus, the .264 USA case is long enough that machine gun links won't be a problem...

[BluntForceTrauma]

You're welcome, John. BTW, "BluntForceTrauma"? Are you trying to tell us something?

Yes, that sometimes the truth hurts!

I found it interesting that case shoulder angle is the same as on the old .30-06 cartridge. I would've expected them to not use the steep, bench rest shoulder of the Grendel, but I'm quite surprised to see them revert to such a shallow angle. Shows an emphasis on feeding/chambering reliability?

Nope, shows an emphasis on play-it-safe, think-inside-the-box approach. All they're losing is "free" case capacity.

To be fair, 6.5 Grendel can't deliver the desired ballistics from the shorter barrels currently favored

Most "desired ballistics" are completely arbitrary, pulled from someone's nether regions to suit some particular whim or fancy. But, hey, when it's a general's arbitrary whim, none of us gets to argue.

The moment you say, "Here's an off-the-shelf with 2600 fps," they'll say, "Nope, we absolutely and unarguably MUST have 2650 fps." The moment you say, "Here's an off-the-shelf that penetrates 16.5 inches," they'll say, "Nope, we absolutely MUST have 16.75 inches. And, oh yes, another $22 million development costs and three more years of employment for all of us to study the issue."

I'm just happy they're s-l-o-w-l-y headed in the right direction. They'll finally climb this Mt. Everest, plant their flag and take their selfie photos, and then they'll notice us already there, lounging around eating crackers and cheese: "Hello, what took you guys so long?"

[LRRPF52]

Cartridges will function in modified, purpose-built AR-10 rifles and magazines in the semi-automatic and fully automatic modes of fire with and without the use of a muzzle-mounted signature suppressor.

It will be interesting to see what changes to the AR10 receiver profile happen along with this.

[stanc]

It will be interesting to see what changes to the AR10 receiver profile happen along with this.

Why would you expect changes to the AR10 receiver profile?

[jurassic]

Why would you expect changes to the AR10 receiver profile?

I beleive Harrison has already designed an built an intermediate AR upper platform (AR12). The dimensions are somewhere between an AR15 and AR10, probably similar in size and weight to the DPMS GII.

[LRRPF52]

Why would you expect changes to the AR10 receiver profile?

If you ever get to fire or handle an original AR10, it feels like an AR15 because the bolt carrier and receivers are much shorter than the 1993-forward AR10's, starting with the SR25. They did that so the BCG tail could articulate inside of an AR15 extension tube. The original AR10 has a much larger diameter extension tube, with a fatter, shorter BCG tail. The weight and balance of those rifles is fantastic-a true infantryman's rifle that just feels great in your hands.

Now that the GII is out, it has gone back to that formula, only using an AR15 diameter BCG that is slightly longer, but much shorter than an SR25 BCG. The GII has made the 1993 receiver and BCG designs obsolete overnight, if you are looking for weight savings, as well as human interface improvement.

[stanc]

The GII has made the 1993 receiver and BCG designs obsolete overnight, if you are looking for weight savings, as well as human interface improvement.

Paul, is that what you meant by possible changes to the AR10 receiver profile? I'm fully aware of the DPMS GII, and agree with you on those design aspects. But the solicitation specified AR10, not any select-fire rifle, so it remains to be seen if the GII would be acceptable. I hope it will be.

[LRRPF52]

Cartridges will function in modified, purpose-built AR-10 rifles and magazines in the semi-automatic and fully automatic modes of fire with and without the use of a muzzle-mounted signature suppressor.

I don't see why a vendor can't use their version of a purpose-built AR10 to fulfill the solicitation. The GII gets back to the original feel and balance of the 1950's AR10's, and based on what I was sensing at SHOT, it really looks like there was an effort in the design and testing to make a 7.62 NATO carbine that would have a chance at passing military durability and MTBF test regimens. Whether or not it can remains to be seen, and their QC record will be the biggest hurdle to overcome.

I know there are a lot of new entrants and old hands in the AR10 market that want to see the GII fail badly.

[stanc]

I don't see why a vendor can't use their version of a purpose-built AR10 to fulfill the solicitation.

Well, what I was thinking is that the GII might not be considered an AR10, what with being somewhat part way between an AR15 and AR10. But, maybe I'm overthinking the matter...

[LRRPF52]

What people in the past 2 generations have grown accustomed to thinking are AR10's, were really a significant departure from the original AR10, especially when looking at weight and balance. This is because of the lengthening of the BCG, which necessitated lengthening of the receivers. Aluminum is light, until you start adding a lot of mass, and SR-25 era receivers are massive. That includes the 1996 "ArmaLite" Inc. (Eagle Arms) AR-10B/T, and the LMT MWS/L129A1.

This whole line of larger AR10's than the original receiver/BCG profile exists for one reason: compatibility with AR15 receiver extension tubes. That was viewed as critical for entry back into the market by Stoner and Reed Knight, has been both overcome, and accommodated with the GII, without having to enlarge the receivers, because they fit an AR15 diameter bolt carrier into a smaller upper receiver, with an enlarged flange around the barrel extension tunnel.

It has taken 21 years since the introduction of the SR-25 to get back to the original design intent that Stoner had, and you really get that sense when you hold and handle one of the original AR10's from the 1950's. It just goes to show that when a good design team thinks outside of the box, and focuses on what can be done, rather than what can't based on certain constraints, something revolutionary can be made.